Small refactor to avoid duplicate __call__ methods in UseMaster & Use…

…Slave

multidb/pinning.py

@@ -95,19 +95,12 @@ def __exit__(self, type, value, tb):
 use_master = UseMaster()
 
 
-class UseSlave(object):
+class UseSlave(UseMaster):
     """A contextmanager/decorator to use the slave database."""
     "Use this in cases where the usual behavior would be to pin to master,"
     "such as when the request method is POST, but you know you're not doing any writing."
     old = False
 
-    def __call__(self, func):
-        @wraps(func)
-        def decorator(*args, **kw):
-            with self:
-                return func(*args, **kw)
-        return decorator
-
     def __enter__(self):
         self.old = this_thread_is_pinned()
         unpin_this_thread()