namespaces: add branches

Note that the exception-catching from the previous branchtip check is moved up
to catch exceptions from the try block surrounding the namespace lookup.

mercurial/context.py

@@ -414,11 +414,6 b' class changectx(basectx):'
                 return
             except KeyError:
                 pass
-
-            try:
-                self._node = repo.branchtip(changeid)
-                self._rev = repo.changelog.rev(self._node)
-                return
             except error.FilteredRepoLookupError:
                 raise
             except error.RepoLookupError:

mercurial/namespaces.py

@@ -44,6 +44,9 b' class namespaces(object):'
         addns("tags",
               lambda repo, name: tolist(repo._tagscache.tags.get(name)))
 
+        addns("branches",
+              lambda repo, name: tolist(repo.branchtip(name)))
+
     def addnamespace(self, namespace, namemap, order=None):
         """
         register a namespace