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.

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)