lock: use '==' instead of 'is' for integer equality ('is' may not work)

mercurial/lock.py

@@ -122,7 +122,7 b' class lock(object):'
     def release(self):
         if self.held > 1:
             self.held -= 1
-        elif self.held is 1:
+        elif self.held == 1:
             self.held = 0
             if self.releasefn:
                 self.releasefn()