check conditions of  make  for equality of variables with an empty value
instead of check definition.
A defined but empty variable under all these conditions results errors.

The message could be confusing.

This one has became direly needed while reworking
Centaurus' pkglists/groups into a tree.

This cp(1) option has been employed already but just for the lists
(and still incomplete as it didn't cover the names coming through
groups mechanism); thanks sem@ for trying out groups/simply/*,
failing to build an image and reporting the problem.
Reported-by: Mikhail Efremov <sem@altlinux.org>

There were heaps of "if type -t git" there already;
it wasn't an unintentional mishap but rather a moderate
copy-paste to get the use cases, and now these seem to
have essentially settled.

So time to scrap some dups.

NB: the scripts in the generated profile can't rely on
the contents of the metaprofile (these need to be able
to work in standalone case either), so a bit of crap
still lurks there.

As too many things started duplicating between distros proper
and (e.g. corresponding) LiveCDs, it became apparent that a class
of entities which end up working for THE_USER (not a sysadmin,
and not a developer, just a Linux user) is in need.

So THE_KMODULES will power installed basesystem and live image,
while THE_PACKAGES, THE_LISTS and THE_GROUPS will participate
in building those.

Typical (to-be-refactored when having settled down)
"cd/git .../cd -" sequences are tweaked to safeguard
against changing back without having actually changed to,
just in case.

features.in/Makefile left with pushd/popd due to its
three-level diving course (which somewhat asks to be
refactores in functions either but is intrinsically
somewhat complex OTOH).

MAIN_GROUPS should align better along with MAIN_PACKAGES
and MAIN_LISTS (even if MAIN_ prefix might be suboptimal
given that these packages are essentially extras within
the particular image).

- better *_LISTS printout
- somewhat cleaner .base comments
- more comprehensible git log messages
  + special handling for complex subprofiles
  + no need to commit build.log ;-)

- image.in/functions.mk: rework kpackage()
  + it takes two arguments explicitly now: this adds some noise
    for "generic" invocations but is rather less messy with recently
    introduced STAGE1_KFLAVOUR (which in its turn is rather cleaner
    than messing with KFLAVOURS, especially since soemthing changed
    in presumably apt and we can't rely on kernel packages being
    installed in the order formed).
- BUILDDIR/DEBUG related fixes
  + Makefile: BUILDDIR initialization moved to distro.mk
- build.log += git info

Renamed server-light.iso into server-ovz.iso to avoid brand dilution
and confusion (rider@'s server-light rather favours kvm, anyways).

Introduced KDEFAULT: a reliable default kernel chooser knob
since apt's regex ordering proved pretty unreliable.
Spelling things explicitly is better anyways.

SYSLINUX related features undergone pretty major rewrite
(that includes syslinux, hdt and memtest).

The problem to tackle was features.in/syslinux/generate.mk
assuming syslinux and pciids available in build *host* system;
this well might not be the case (or worse yet, those can be
just different).  So now we're a bit less elegant and a bit
more enterprise, stuffing things into chroot and working there.

Bunch of other fixes along the road, including ; to name a few:
- fixed memtest entry (overlooked while renaming SYSLINUX_ITEMS)
- new and shiny doc/CodingStyle
- gfxboot, stage1 target chain, hdt tweaks
- distro.mk rehashed
- README++
- TODO: dropped (integer overflow anyways)
  + actually moved off-tree to reduce commit spam
- s,\.config\.mk,distcfg.mk,g
- doc/profiles.mk.sample: sample ~/.mkimage/profiles.mk
- ...and assorted fixups/additions

Sorry for convoluted commit, this would have been pretty hard to
rework into some really readable shape (and you might be interested
in the original repo's history horrors then, anyways).

- more thorough build stages inline doc
- quieter BUILDDIR instantiation
- branding-altlinux-sisyphus by default
- prettify installer selection somewhat
- mkimage #24669 fixed upstream
- sub.in/stage1/modules: +drm (as in m-p-d, for KMS)
- tags2lists: generalize a bit

Also included:
- reworked syslinux feature inclusion
- syslinux: s/textprompt/prompt/
- README++

...along with obituary fixes.