basectx: move __repr__ from changectx

We change the hardcoded 'changectx' to instead use type(self).__name__ so that
objects that inherit from basectx in the future will be able to use the same
representation.

mercurial/context.py

@@ -41,6 +41,9 b' class basectx(object):'
     def __int__(self):
         return self.rev()
 
+    def __repr__(self):
+        return "<%s %s>" % (type(self).__name__, str(self))
+
     def rev(self):
         return self._rev
     def node(self):
@@ -153,9 +156,6 b' class changectx(basectx):'
         raise error.RepoLookupError(
             _("unknown revision '%s'") % changeid)
 
-    def __repr__(self):
-        return "<changectx %s>" % str(self)
-
     def __hash__(self):
         try:
             return hash(self._rev)