Debian Jessie is now running git 2.0.0.rc0 - fix tests for it

Should remove the version calculation call from GitAPITestCase, since
it is now available as a standard part of CliGitAPIImpl, and only
makes sense in the context of CLI based references.
Merge commit '8d41aafb80a8d2aa957c13d9d72f6ba9cf9a0fa6' into HEAD