Since the config was created in live, it remained after installation.
Now the config will be created at the first start of live and only
if /image/ALTLinux/ is present (it will not be available when
bootloading via http or ftp). After installing live, the package will
be deleted and the config will not be created at the first start.

This variable blocks the enable of online repositories and activates
the enable of RPMS.main repository in iso or rootfs.
The old name was misleading.

Default changed from yandex to alt due to:
https://bugzilla.altlinux.org/show_bug.cgi?id=41588#c1

use/repo/main for vm targets will now create and enable the main
repository in /ALTLinux on rootfs.

This is to make building addon images possible;
those carrying packages but lacking any stage2.

Those few places lacking "; @:" replacement for a real recipe
have been finally -spotted- identified with `make check'
and fixed.

Just a hook to export alt-gpgkeys pubring data.

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...

We've got some parts of it in build-distro feature,
and some went to dev feature for no real reason.

But a bare installer might go without package base,
and LiveCDs other than live-builder might find local
repository useful given aufs2 root overlay.

Now the overall scheme is more straightforward:
- a distro:
  + asks that a package repo be included
  + cares to further add the packages to it
- a repo feature:
  + pulls in sub/main for it to happen
  + provides genbasedir script to create repo metadata
  + supplements live feature with repo configuration