namespaces: make the constructor into named args

namespaces: make the constructor into named args

None of the arguments are truly optional but this makes adding future arguments
more robust and perhaps optional.

--- a/mercurial/namespaces.py	Thu Jan 15 20:36:03 2015 -0800
+++ b/mercurial/namespaces.py	Wed Jan 14 19:39:13 2015 -0800
@@ -120,12 +120,13 @@
 
     """
 
-    def __init__(self, name, templatename, listnames, namemap, nodemap):
+    def __init__(self, name, templatename=None, listnames=None, namemap=None,
+                 nodemap=None):
         """create a namespace
 
         name: the namespace to be registered (in plural form)
+        templatename: the name to use for templating
         listnames: function to list all names
-        templatename: the name to use for templating
         namemap: function that inputs a node, output name(s)
         nodemap: function that inputs a name, output node(s)