git: show the version of `pygit2` with verbose version output This seems like useful info to have when debugging. I followed the precedent of hg-git, which prints something like: hggit external 0.9.0a1 (dulwich 0.19.15) We don't have a version number assigned (because it's internal), so it's just the parenthetical. Differential Revision: https://phab.mercurial-scm.org/D9436