The 'splash=0' parameter not only disables splash, but also switches
to tty5 on which plymouth is supposed to run. This looks like a bug
in propagator. 'nosplash' is also a general parameter for propagator
and make-initrd.

For install2, this is needed to work around error 99-cdrom.sh with method:cdrom.
The error shows up with make-initrd-bootchain, but not propagator, as lowmem is
enabled for propagator in this mode.
For rescue, the point is that the latter has become quite large, so by default
it would be better that way.

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

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.

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

- parameter order fixed to "simple first, then those with args"
  and documented as the preferred one (might be debatable, okay)
- added "lowmem" to live so it avoids a ramdisk but works off media
  (it's a knob for propagator)
- added "fastboot" everywhere (but failsafe install) to make use
  of Linux 2.6.29+ async controller initialization
- every snippet got a trailing newline so that isolinux.cfg is readable

And a fancy makefile to check for shortcut dups!

Implementation based on m-p-d::profiles/scripts.d/03-syslinux
(but heavily modified for m-p of course)

NB: this implementation is awfully cut-n-paste one,
there are lots of common code with install2
which are subject to careful surgery

Now we don't dump all the gory details onto thee
but rather log them handsomely and present only
the most important details by default; use DEBUG=1
and/or BUILDLOG=/path/to/file to tweak.

Also introduced IMAGEDIR and IMAGENAME.

The rest:
- ovz-smp is no more
- base-l10n pkglist (suggested by Alexander Kuprin)
- clean.mk:
  + fixed an oversight: the test result erroneously applied
    only to the first command of several ones that should be
    run iff build/ is a symlink
  + drop implicit rules (it's no C code)
- Makefile: more reasonable iso names
- image.in/Makefile: .disk/date too

- get rid of $dest
- work on features.in/syslinux
- README++