phase: invalidate the phase's set cache alongside the revs

Invalidate was leaving set data around leading to possible bugs in revset.

mercurial/phases.py

@@ -209,6 +209,7 b' class phasecache(object):'
 
     def invalidate(self):
         self._phaserevs = None
+        self._phasesets = None
 
     def _populatephaseroots(self, repo):
         """Fills the _phaserevs cache with phases for the roots.