Created a copy of tests/resources/testrepo.git that is compatible
with the Clar sandboxing helpers.
Restructured commit test suites to use Clar sandbox helpers.
Now using typed data arrays rather than lots of macros to define test
cases.
git_commit_create is supposed to update the given reference
"update_ref", but segfaulted in case of a yet to be born
reference. Fix it.
Signed-off-by: schu <schu-github@schulog.org>
