revlog: return the nodemap as the nodecache

Ultimately, the nodecache is the nodemap. To stop having this disctinction, we
start using the nodemap where the nodecache was used.

This work is part of a refactoring to unify the revlog index and the nodemap.
This unification prepare the use of a persistent nodemap.

Differential Revision: https://phab.mercurial-scm.org/D7316

mercurial/revlog.py

@@ -630,7 +630,7 b' class revlog(object):'
             # populate mapping down to the initial node
             node0 = self.index[0][7]  # get around changelog filtering
             self.rev(node0)
-        return self._nodecache
+        return self.index.nodemap
 
     def hasnode(self, node):
         try: