Old package expression had two problems:
* source download link was broken
* when working, it downloaded almost 400 MB of data because it cloned
the entire mercurial repo, via http it's only about 140 MB.
[Bjørn: extend commit message]
Basically it builds, but I still don't know how to run it. I imagine the
installPhase is still too poor, but it's better than nothing.
I also added two mygui versions. That stable, and that required by Rigs of Roads (svn).
svn path=/nixpkgs/trunk/; revision=26618