Fix for leaking file descriptor issue

Add call to stopTrying on the APNSClientFactory (ReconnectingClientFactory) in the timed
disconnect portion of the code.  If this call is not made, the reconnecting code will
reconnect to Apple and the connection is left unreferenced. This can cause an issue
with 'Too many open files'.

pyapns/server.py

@@ -208,6 +208,7 @@ def write(self, notifications):
             if conn_time > MAX_CONNECTION_TIME:
             	log.msg('APNSService write (disconnecting based on max connection time)')
                 self.factory.clientProtocol.transport.loseConnection()
+                self.factory.stopTrying()
                 self.factory = None
 
         if not self.factory: