Clean up asserts in Tree.

Document the types of arguments to various tree methods instead of
asserting. In particular, these asserts were causing failures in
python2.4, when reading modes from the index resulted in a long rather
than an int. This is harmless, so the asserts were just dropped.

Change-Id: I4a8f8b1527e0fd9571ebdb760e09230f25ac3918
Implement set_symbolic_ref separately in Disk/DictRefsContainer.

When writing tests, it became clear that the old implementation was broken.

Change-Id: Id98d7af0c92568d1faf555784214d0c1eb298feb
Move tests that build repos from scratch to their own class.

Change-Id: I7950ed60fedb7098c3db2a63cc1f9ba14d1c1fa2
Allow double-staging of files that are deleted in the index.

Change-Id: I92b75d09281d37c2486f77aa52680b8173379016
Add docstring.
Make sure ids get updated when the object changes.
client: move parsing report-status data into a method

This makes send_pack shorter and less indent-heavy, making a following change
which will require wrapping that code in a try/finally more readable.

Change-Id: I1e3d4d0d79ee61ec0b06dd2c4362c7b113072124
Merge improvements and extra tests, mainly to deal better with creating non-bare repositories.
dulwich.client: fix fetch if no progress function is specified

Change-Id: I0627b9bea8d7259984fb6587a877bb027dde7367
Remove PackData.__del__ as it causes reference loops; use PackData.close
instead.
compat.test_client: test fetching packs

Change-Id: Ib7b271dd30265ea6633fece8c04566165fd8ce84
client: fix send_pack when there is nothing to send

Includes a functional test that failed prior to this fix.

Change-Id: I7d95cff21c56a198a836479d8e88a3589e0f196c
repo: clean up whitespace
DiskRefsContainer: don't crash deleting a ref without peeled refs

It's a valid state to have loaded packed refs but not have any peeled
refs. Prior to this change, attempting to delete a tag in that
configuration would cause a traceback when checking 'if name in
self._peeled_refs' since self._peeled_refs was None.

Change-Id: I442d8dd4c97316c6295c9dbdace088feeedddd35
test_repository: clean up whitespace

Change-Id: I5b6406dd16b9e6d2cac2061dc3f0eeb8cebce3ce
test_repository: test packed ref deletion with no peeled refs

Change-Id: I996f70f8f2433673a5ee74b8b0145035bf4809a2
Merge fix for send pack when there is nothing to fetch from Augie.
Merge fix for crash deleting a ref.
Merge some extra tests for packed ref deletion with no peeled refs
Update NEWS.