Forward project directory to source services.

Forward project directory to source services.
This helps to implement an efficient way to create source tarballs from Git repositories:
1. The cloned Git repository will be stored only once in a directory; all projects will use this repository (determined by the URL).
2. The bzip2 compressed tarball will be created via 'git archive $branch $filestoinclude --prefix=$name | bzip2 --best >$projdir/$name-$version'.
3. The version will be adapted automatically without the set_version service.
4. All branched/linked projects will be updated automatically (does not with current implementation).
5. Not to mention it saves space on source host(s).