Log Message:
py-dulwich: updated to 0.19.12

0.19.12:
BUG FIXES
* Update directory detection for get_unstaged_changes for Python 3.
* Add a basic porcelain.clean.
* Fix output format of porcelain.diff to match that of
  C Git
* Return a 404 not found error when repository is not found.
* Mark .git directories as hidden on Windows.
* Implement RefsContainer.__iter__
* Don't trust modes if they can't be modified after a file has been created.