changegroup: assign to proper attribute

0548f696795b accidentally assigned to self.clrevtolocalrev instead of
self._clrevtolocalrev. Surprisingly, no tests failed as a result of
this mistake. Curious.

Differential Revision: https://phab.mercurial-scm.org/D4144

mercurial/changegroup.py

@@ -605,7 +605,7 b' class cgpacker(object):'
         # Ellipses serving mode.
         self._clrevtolocalrev.clear()
         if self._nextclrevtolocalrev:
-            self.clrevtolocalrev = self._nextclrevtolocalrev
+            self._clrevtolocalrev = self._nextclrevtolocalrev
             self._nextclrevtolocalrev.clear()
         self._changelogdone = True