committablectx: move __contains__ into workingctx

This was mistakenly moved from workingctx to committablectx in
9d56a3359011. Since the method is querying the dirstate, the only logical place
is for it to reside is in workingctx.

mercurial/context.py

@@ -976,9 +976,6 b' class committablectx(basectx):'
     def __nonzero__(self):
         return True
 
-    def __contains__(self, key):
-        return self._repo.dirstate[key] not in "?r"
-
     def _buildflagfunc(self):
         # Create a fallback function for getting file flags when the
         # filesystem doesn't support them
@@ -1179,6 +1176,9 b' class workingctx(committablectx):'
             if d[f] != 'r':
                 yield f
 
+    def __contains__(self, key):
+        return self._repo.dirstate[key] not in "?r"
+
     @propertycache
     def _parents(self):
         p = self._repo.dirstate.parents()