* Fix NameError when encountering errors during HTTP operation.
(Jelmer Vernooij, 1208)
* Raise exception when default identity can't be found.
(Jelmer Vernooij)
* Add a dedicated exception class for unresolved
deltas. (Jelmer Vernooij, 1221)
* Support credentials in proxy URL. (Jelmer Vernooij, 1227)
* Add ``dulwich.porcelain.for_each_ref``. (Daniele Trifirò)