Still have to refer to MCST instead at the moment...

Fixes: f1c5f98795a698fdd665c7286f15d6e023195200

SYSLINUX happens where GRUB happens too, just in case.

The problem at hand is that some branding-*-bootloader tend to
*create* /etc/sysconfig/grub2 without bothering to check that it
existed, thus confusing the subsequent scripts (e.g. 65-serial.sh
tries to run update-grub that's just absent then).

Have to refer to MCST instead at the moment.

See-also: c0c5c94b

Partially this is a return of the commit 35db7537.
For branding packages, regexp is used. Therefore, it makes no sense to limit them
to architectures. use/plymouth and use/syslinux was fenced separately.

Plymouth is (much more) portable, but our branding packages contain
bootsplash designs only on x86 nowdays.

There's an ISO9660 COPY tag for license info file;
make use of it, factoring use/docs/license out
while at that.

One of the goals was to make it hold the reference
to reference to GPL in regular builds and starterkits
;-)

Added use/branding/slideshow/once as one of the uses
albeit the interface is universal; see this page for
more info: http://altlinux.org/branding/slideshow [ru]

branding-*-bootloader was handled for stage1 by syslinux feature
but somehow got missed regarding the installed system; let's fix.

An initial draft of it was done half a year ago but several tricky
thingies had kept the code from showing up as it was rather brittle
and incomplete.

This implementation involves quite a few changes all over the place
but finally works good enough for live and installer images.

Please pay attention to the versions of these packages:
- installer-feature-setup-plymouth (0.3.2-alt1+)
- branding-altlinux-sisyphus (20110706-alt2+ if used)
- plymouth (0.8.3-alt20.git20110406+)

See also:
- http://www.altlinux.org/Branding
- http://www.altlinux.org/Plymouth

NB: for the feature to work properly the chosen branding
package set should have proper Provides: and Conflicts:,
specifically it must explicitly conflict with the most
lexicographically cool package set around (these days
it's sisyphus-server-light).

As duly noted by glebfm@, branding issues need more attention
by now since only stage1/install2 got some of it so far in this
regard.  Hence the dedicated feature comes to the rescue
(well no, it doesn't actually mess with rescue!).