[PATCH 13 of 14 RFC] memfilectx: add _filerev method

[Sean Farley]

# HG changeset patch
# User Sean Farley <sean.michael.farley at gmail.com>
# Date 1373325777 18000
#      Mon Jul 08 18:22:57 2013 -0500
# Node ID 3f63ecaf71d993eb929cb12cafc96fc01e7c216d
# Parent  56574c855bf31605fc2f7a696181f9d84a7eb64f
memfilectx: add _filerev method

diff --git a/mercurial/context.py b/mercurial/context.py
--- a/mercurial/context.py
+++ b/mercurial/context.py
@@ -1381,10 +1381,12 @@
         return 'x' in self._flags
     def islink(self):
         return 'l' in self._flags
     def renamed(self):
         return self._copied
+    def _filerev(self):
+        return None
 
     def cmp(self, fctx):
         """compare with other file context or workingfile context
 
         returns True if different than fctx.