contrib/win32/mercurial.ico

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

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