adding my updates to git_repository, includes Dylan's unmerged additions

<b>Please</b> merge Dylan's(drunkel) request first and then allow me to update this request.

Adds functionality for self.open, self.access, and self.delete.
I added the husks of all the methods from /lib/repo/subversion_repository.rb we can't reuse. Also adds the methods from /lib/repo/subversion_repository.rb we can potentially reuse unaltered.