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 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.

"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).

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...

A variant of rescue that marks the need to be careful
towards block devices and filesystems thus reducing
the amount of auto-activation done by startup-rescue
(0.17 or newer).