Log Message:
py-dulwich: updated to 0.9.11

0.19.11:
IMPROVEMENTS
* Use fullname from gecos field, if available.
* Support GIT_AUTHOR_NAME / GIT_AUTHOR_EMAIL.
* Add support for short ids in parse_commit.
* Add support for prune and prune_tags arguments
  to porcelain.fetch.

BUG FIXES
 * Fix handling of race conditions when new packs appear.