If set then don't remove apt and rpm from live images.

It's needed for alterator-wizardface ported to guile22.
Suggested-by: Sergey Bolshakov <sbolshakov@altlinux.org>

The problem at hand was that an installer component
of a "DVD class" image does use/cleanup/installer
while installable LiveCD component gets broken by that
(livecd-install -> installer-scripts-remount-stage2
which gets removed as installer-*).

Split those.

This one has been introduced by alterator-users update;
makes no sense on its own, just drop.

This is based on distro/regular-jeos but torn into two
and somewhat updated for sisyphus-going-to-bring-p8:
1) libcap-ng is now required by util-linux;
2) bridge-utils might be needed for subsequent images.

The installer feature added is a trivial wrapper around
apt-cache nodeps to uninstall the ^lib packages that have
no more dependencies upon those when the temporarily
installed packages like alterator-browser-qt get removed.

A few more leftover libraries tend to hang around after
purging extra alterator packages that have fired already
during installation stage3; this change might hurt someone,
please do notify if that is the case (OTOH one isn't forced
to use it or to inherit intermediate targets that do so).

A few too many downstream makefiles employed the pattern
of "export GLOBAL_VAR := $(VAR)"; macroize that.

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...

This is a sort of anti-feature which removes and not builds;
still with mkimage-profiles' approach we can at least build
up the removal procedures as well.

It's what triggered the tagged scripts, BTW.