namespaces: add method to get template name of namespace

This patch adds the public api for getting the template name of a namespace so
that the next patch can use it to generate a template keyword automatically.

mercurial/namespaces.py

@@ -84,3 +84,7 b' class namespaces(object):'
                     return cl.node(maxrev)
                 return n[0]
         raise KeyError(_('no such name: %s') % name)
+
+    def templatename(self, namespace):
+        """method that returns the template name of a namespace"""
+        return self._names[namespace]['templatename']