blackbox: log incoming changes via ui.log()

Logs incoming changes to a repo to ui.log(). Includes the number of changes
and the hashes of the heads after the new changes.

Example log line:
2013/02/09 08:35:19 durham> 1 incoming changes - new heads: cb9a9f314b8b

Currently the blackbox logs the unix user that is performing the push/pull.
It would be nice to log the http authorized user as well so it works with
hgweb, but that's outside the scope of this commit.

mercurial/localrepo.py

@@ -2399,6 +2399,12 b' class localrepository(object):'
                     for n in added:
                         self.hook("incoming", node=hex(n), source=srctype,
                                   url=url)
+
+                    heads = self.heads()
+                    self.ui.log("incoming",
+                                _("%s incoming changes - new heads: %s\n"),
+                                len(added),
+                                ', '.join([hex(c[:6]) for c in heads]))
                 self._afterlock(runhooks)
 
         finally: