New versioning system, not dependent on SVN.

The macro VERSION is now defined by the build script, rather than
relying on SVN keyword substitution. Also, there's a new --version
option which actually uses it (previously it was never used for
anything!).


git-svn-id: svn://svn.tartarus.org/sgt@10261 cda61777-01e9-0310-a592-d414129be87e