index: use `index.rev` in `revlog.rev`

Differential Revision: https://phab.mercurial-scm.org/D7325

mercurial/revlog.py

@@ -687,7 +687,7 b' class revlog(object):'
 
     def rev(self, node):
         try:
-            return self.index.nodemap[node]
+            return self.index.rev(node)
         except TypeError:
             raise
         except error.RevlogError: