Do not create syslinux.cfg if EFI_BOOTLOADER is set to not equal grub-efi.

These are partial commits reverts:
01ee4075
e42bcdcb
5cfc7ede

The scripts were named the same for syslinux and grub. Because of this,
scripts for syslinux were overwritten by grub scripts.

...so that bits required for PXE boot are handy in the image.

Suggested-by: glebfm@altlinux.org, klark@altlinux.org

I've just borrowed glebfm@'s one introduced by commit
ec23a8ec before; this
still might be improved it seems.
Suggested-by: Gleb Fotengauer-Malinovskiy <glebfm@altlinux.org>

Every .iso was assumed to be bootable since the very beginning[*],
and isoboot images were deemed to be x86 isolinux ones; this didn't
change with basic ppc/armh support as I never ran into hardware
that would _boot_ those ISOs, not only run the code, and it was
only e2k isodata project that finally forced this refactoring.

It's still not perfect: pack and syslinux features still end up
somewhat interwoven, and too much places care for architecture
the image is being built for (instead of archdep features tossing
their appropriate bits and pieces in).

Should help:
- any-arch regarding isodata images;
- {x86,aarch64}/efi by decoupling isoboot and isolinux;
- ppc{,64} as introducing yaboot support will be easier now;
- mipsel{,64} too, hopefully.

* I knew of school addon images baked with mkimage-profiles-desktop
  but postponed and then neglected the whole problem for years...

This is more appropriate default value nowaday.

Should be a (slightly cleaner) no-op.

These happened to collide after initial copypaste
of 20install2.cfg snippet, spotted that recently.

This one enables rw session support for Rescue images;
the nitpick is that syslinux' gfxboot *will* set this up
when booting the same ISO from USB Flash media instead of
optical one (CD/DVD-ROM/RW), and we don't put gfxboot into
a standalone rescue image.

See-also: http://altlinux.org/propagator
See-also: http://altlinux.org/remount_rw

A one-liner for syslinux and a simple installer feature
change a lot in this regard!

Was broken in too many places including several libraries
x11vnc currently links against getting removed, several
utilities missing, and no way to guess what to do...

One could stumble upon http://altlinux.org/vncinst
or find the implementation in installer.git but it's
not exactly user-friendly.

Turns out it's "splash=0" that does the job.
Suggested-by: Lenar Shakirov <snejok@altlinux.org>
See-also: https://bugzilla.altlinux.org/28625

...instead of hardwired 0x314 (which is rather wrong
for modern kernels and hardware, just ran into that
with yet another Matrox G200eW WPCM450).

s/ALT Linux/ALT/g as per s/ALT Linux/BaseALT/g Ltd

This one is related to forensics mode handling in mkimage:
there's a regex that's expecting the old string ending with
hash value, and it stops working when this is changed here
(at least as of mkimage 0.2.18).

So partially undo the change for this particular file to avoid
refind's example menu for regular-rescue.iso (or any other image
involving forensics mode), and hope to revert this commit some day.

This keyword was misused due to the lack of understanding
of its meaning; thanks zerg@ for the hint, let's hide the
kernel boot parameters not expected to be modified by user
under the hood (and vice versa in some cases).

Note that this is just a keyword shift in all cases
but mediacheck where "showopts" is now added.

NB: this keyword is only relevant for gfxboot.

"Failsafe install" disabling APIC/LAPIC looks somewhat obsolete
by now; the only reasonable part seems to be the attempt to force
VESA videodriver for the installer (should be done within installer
itself though).

...to *not* error out if there's no gfxboot at all.

"Forensic mode" submenu has fallen apart after the original commit
as the tricky logic in mkimage::tools/mki-copy-efiboot failed to
pick up the new variant; this should all be redone (solo@ has
started doing something but it needs a time-consuming review).

Fixes: 79d02088

This one is just like STAGE2_BOOTARGS but for rescue images
(which don't do that one for quite a few reasons).

This one was an experimental but the server is long
offline and isn't going back up; remove the obsolete
config snippet, if/when it's done again it's the easiest
part to be restored (the implementation should provide
HTTP/FTP/NFS-publishable deliverables without the need
to extract those from ISO images).

There's a convention that syslinux configuration snippets
carrying the names of subprofiles involved are picked up
automatically; there were a few special cases already
when this is actually inconvenient, and there's another
one at hand so let's just step up and do it.

NB: this is a sort of a hacky hook though, wish an elegant
    interface would come to mind some day.

This one provides cmdline arguments for startup-rescue >= 0.24
which would bring up networking and sshd in its turn thus allowing
remote access to the host booted in this mode.

The feature has been asked for by many people including mithraen@
and valintinr@ (and I'd make use of it another day too).

See the appropriate startup-rescue commit description for notes
on implementation; this default set of variable values should be
both useful and illustrative though.

...just like any other stage2 based boot target,
both for consistency and specifically for propagator
test image.

The former approach to handling "LiveCD with sessions"
has been to mangle "automatic=method:cdrom" into
"automatic=method:disk,label:ALT*" within gfxboot
so that propagator and make-initrd-propagator would
try and discover/create a filesystem labelled
"alt-live-storage" on a LiveFlash's free space.

Then "live_rw" handling has been unified in
make-initrd-propagator (as of 0.18-alt1) to accept
any of "label" subparameter or "live_rw" argument
to go and create_disk_slice().

Then propagator's cdrom.c has been fixed to actually
try sdX1 before sdX (as of 20150306-alt1).

And now it's all been tested to verify that:
- flash "ro" and "rw" boot is OK
- CD-ROM "ro" boot is OK
- CD-ROM "rw" boot is fine given that there's
  a partition labeled "alt-live-storage" elsewhere

This is a can of worms indeed :-/

References
~~~~~~~~~~
* http://altlinux.org/initrd-propagator
* http://altlinux.org/make-initrd-propagator
* http://bugzilla.altlinux.org/28289

This one has been inspired by these guys:

  http://www.informatimago.com/linux/emacs-on-user-mode-linux.html
  https://raymii.org/s/blog/Vim_as_PID_1_Boot_to_Vim.html

It's aimed at building images running their main userspace
piece instead of ramdisk's init, that means PID=1, UID=0.

Mostly fun of course but it suddenly became interesting with
kernel IP autoconfiguration and e.g. elinks running this way
(NB: requires patched make-initrd 0.8.8 at the moment to get
resolver configured).

And startup times are way better than sysvinit and systemd combined!

cfg.in/README should be explicit regarding
"automatic=method:cdrom" being usable for
flash media too (propagator has been fixed
since 20101130-alt10 or so, and gfxboot is
able to tweak the cmdline having figured
out it's running off the flash either).

It's not neccessarily installation media.

Shift boot order so that rescue image can get mediacheck too
but still boot into rescue by default.

As proposed by Maxim Suhanov since there are only
7 loop devices available upon bootup which might be
not enough given ro,loop mounts by default.

This value is used to authenticate rescue rootfs image
by verifying the squashfs file's sha256sum before use
(propagator-20140419+).

Looks like this check might be useful for other stage2
images as well but let's get started with this one.

Thanks Maxim Suhanov <suhanov/group-ib.ru> for both
http://www.forensicswiki.org/wiki/Forensic_Live_CD_issues
and propagator patches.

Thanks Maxim Suhanov (suhanov <AT> group-ib.ru,
http://www.forensicswiki.org/wiki/User:.FUF)
for taking the time to review regular-rescue image.

Note that there are more than just filesystems:
arrays, logical volumes and swaps aren't activated either;
startup-rescue >= 0.18 should make that clear enough.

syslinux shortcut handling is case-insensitive,
let's find yet another letter...