su wasn't making it into the image breaking ~/.git setup,
and there's no reason for a full default boot timeout either.

It looks like the intermediate targets aren't all equal:
some define a finished feature while some create a common
lower level piece of configuration.

Let's do shortcuts for the former so that a distro line can be
more terse and descriptive; help targets in features.in/ tweaked
accordingly.

If there's an ethernet interface, a DHCP client, and these
can result in connectivity out-of-box, then it's rather
a feature for almost any LiveCD.

Thus the configuration script is moved from dev feature
to live one with the addition of dhcpcd/dhclient test.
This is asking for some more neat solution though...

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.

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

If you make distro/live-builder.iso, the result is an image
containing almost everything (short of actual full enough
repository) to rebuild itself.  It will attempt to configure
eth0 with DHCP and reach http://ftp.altlinux.org for packages.

RAM requirements start with 2Gb, self-build is accomplished
on a 4Gb host with "make CLEAN=1 distro/live-builder.iso".

Packages required for "make distro/syslinux.iso" get included.

(some due fixups all over the place too)