lock: the correct way to do a trylock() is to use a timeout of 0

mercurial/lock.py

@@ -112,8 +112,7 b' class lock(object):'
         # if locker dead, break lock.  must do this with another lock
         # held, or can race and break valid lock.
         try:
-            l = lock(self.f + '.break')
-            l.trylock()
+            l = lock(self.f + '.break', timeout=0)
             os.unlink(self.f)
             l.release()
         except error.LockError: