Log Message:
py-dulwich: updated to 0.19.16

0.19.16:
* Don't send "deepen None" to server if graph walker
  supports shallow.

* Support tweaking the compression level for
  loose objects through the "core.looseCompression" and
  "core.compression" settings.

* Support tweaking the compression level for
  pack objects through the "core.packCompression" and
  "core.compression" settings.

* Add a "dulwich.contrib.diffstat" module.