Fix flaky/failing tests introduced in the last few changes.

Change-Id: Ie87a60d970638c4682970a9b4f47d8240de49532

dulwich/repo.py

@@ -402,6 +402,7 @@ class DiskRefsContainer(RefsContainer):
         """
         self._check_refname(name)
         filename = self.refpath(name)
+        ensure_dir_exists(os.path.dirname(filename))
         f = GitFile(filename, 'wb')
         try:
             if old_ref is not None:

dulwich/tests/test_server.py

@@ -202,7 +202,7 @@ class ProtocolGraphWalkerTestCase(TestCase):
         self.assertRaises(GitProtocolError, self._walker.determine_wants, heads)
 
         self._walker.proto.set_output([])
-        self.assertRaises(GitProtocolError, self._walker.determine_wants, heads)
+        self.assertEquals([], self._walker.determine_wants(heads))
 
         self._walker.proto.set_output(['want %s multi_ack' % ONE, 'foo'])
         self.assertRaises(GitProtocolError, self._walker.determine_wants, heads)