git: fix pull request deletion - don't crash on deleting refs to PR heads The refs name was passed as unicode string, and that would cause failure like: File ".../site-packages/dulwich/repo.py", line 720, in __delitem__ if name.startswith(b"refs/") or name == b"HEAD": TypeError: startswith first arg must be str or a tuple of str, not bytes Fixed by correctly passing the ref name as bytes, as we do when creating the PR refs. Tests added by Mads Kiilerich.

# requirements.txt file for use as "pip install -r requirements.txt" as a
# readthedocs compatible alternative to "pip install -e ." which is a working
# alternative to "setup.py develop" which doesn't work with Mercurial 3.7
.