setup: use printf instead of print Yuya Nishihara pointed `printf` to me, so I will respect the cargo cult.

git: don't fail import when pygit2 is not install `test-duplicateoptions.py` was failing on py2 for be because I didn't have pygit2 installed. It failed because we depend on pygit2 at import time. This patch makes it so we successfully load the git extension even if pygit2 doesn't exist -- we just won't be able to use it in that case. Differential Revision: https://phab.mercurial-scm.org/D8268