convert: test for shell injection in git calls (SEC) CVE-2016-3069 (5/5) Before recent refactoring we were not escaping calls to git at all which made such injections possible. Let's have a test for that to avoid this problem in the future. Reported by Blake Burkhart.

To run the tests, do:

cd tests/
python run-tests.py

See https://mercurial-scm.org/wiki/WritingTests for
more information on writing tests.