Merged new configuration system

Merged new configuration system

The normal way of using 0compile has changed. Before, it selected a set
of versions at setup time and stayed with them unless you ran setup
again.

Now, it chooses the best versions each time you build. If the versions
have changed, it will say what has changed and abort. You can use:

--clean for a clean build (slow but safe),

--force to use the new versions without cleaning (fast but unsafe), or

you can copy the previous version (the build-environment.xml file)
somewhere safe and tell it to use those versions (set the "selections"
line in 0compile.properties to its path).

Also, the target directory no longer includes the version number, just
the name and architecture (e.g. "gnu-hello-linux-x86_64"). Before, you
could end up will multiple target directories, which was confusing,
especially if you registered the old one using "0launch --feed".

Together, these changes make it much easier to track updates in the
source code and dependencies.