There was some extra duplication, just clean it up.

This further refines the modular build by making
metadata being a clearly separated feature rather
than having to rely on runtime tests, and also by
moving the code which cares for kernel bits of base
installation (.base list) in a feature of its own.

There's more to it but let's get the ball rolling first.

The missing part so far is passing "lang=ab_CD" to the kernel;
it's done with gfxboot and is somewhat doable without it...

"Alien" rather means "CentOS-based" than "xenophilic" here;
in case you still wonder: http://www.altlinux.org/Hasher/CentOS

As was noted by Alexey Shabalin in libosinfo context,
current ALT Linux images tend to lack ISO9660 metadata
-- which they did have back in the day of Master 2.4.

Please note that the data collection occurs this way
due to mkimage's config.mk resetting the values to be
empty; this was worked around by using another config
file, $(BUILDDIR)lib/iso.mk, and including it later
but that would require a separate target with per-target
CONFIG variable which isn't elegant at all given the need
to actually build up the metadata set.

So the variables were changed (to be more readable anyways)
and then proxied back to BOOT_*.  This might be cleaned up
some day after the inclusion order is tweaked or mkimage
defaults get set-if-unset-yet (?=).

A minimal chroot supporting extension via apt-get;
vitals if built on Sisyphus as of Jan 16, 2012:

  i586: 13M tar.xz, 58M chroot (33M w/o /usr/share/{doc,locale,man})
x86_64: 14M tar.xz, 60M chroot (35M w/o /usr/share/{doc,locale,man})

Trivial fixups (extra checks) added to two script hooks.

At least it shouldn't bail out when the anticipated file
just isn't there...

Initial openSUSE package base taming effort has shown that
relatively few things should be fixed; subst has been generalized
as -i option to sed(1) since its introduction, so let's just fix it.

Several targets were used in a duplicated way
that made no harm but no sense either.

Actually this is the proper rewrite that was looming ever since
tgz support was introduced: there are multiple archive formats
supported by mkimage, and there are multiple compression methods
available as well.

So the bullet got bitten yet again along with the "goal parser"
which should be more straightforward by now.

Thanks dkr@ and mithraen@ for the inspiration of this evening.

The features might get copy-pasted (or even copied-and-pruned)
when initialized; there's an unneccessary duplication of the
function name in the line adding it to FEATURES list, thus
prone to being forgotten and causing some havoc later on.

It was wrong in the first place but tackling this with some
double-colon rules ran into terminality issues, and further
tortures were considered unneccessary.

The current solution isn't perfect (no completely transparent
function name registration upon corresponding target being called)
but at least it is an improvement...

It is a current convention to prefer clearly phony targets
(see the wiki page) so let's follow it here too.

This is quite a large-scale change since mkimage-profiles got used to
baking distributions over the last year, and virtual environments are
quite different, so e.g. image.in/Makefile had to be split in two with
the main part of it moved into features.in/iso/lib/.

Short overview:

- features.in/Makefile: lib/ support
  (supporting VE images requires dynamic modifications
  to image.in/Makefile before starting the build;
  the most natural way to achieve that seems to use
  features mechanism along with makefile include dir)

- packaging format related part moved into features.in/pack
  (should be better prepared for diversity either)
- features.in/iso renamed to features.in/build-distro
- features.in/ve  renamed to features.in/build-ve
  + NB: these could not be merged as e.g. features.in/build
    due to completely different script hooks

- lib/image.mk renamed to lib/build.mk
- image, config, log postprocessing moved downstream
- added a sort of a topping in the form of lib/sugar.mk
- assorted style fixups (like ifeq usage)

- clean.mk: reliability fix (the problem was observed by Oleg Ivanov
  and me too but finally it did get the attention quantum)

- reviewed, updated and extended docs
  + QUICKSTART: should be[come] a step-by-step guide
    (thanks Leo-sp50 for prodiving feedback)