version.sh: handle shallow clones and snapshots.

version.sh: handle shallow clones and snapshots.

Shallow clones (--depth X) lack the N tag used to compute
the revision number: use 'git-YYYY-MM-DD-hhhhhhh' as revision,
where hhhhhhh is the short git hash.

Snapshots from gitweb do not have git information at all,
but they have the short git hash in the directory name:
append it to the release number.