Quick update to the error message on a 503 to reflect that they can happen on maintenance or when servers are overloaded.

Author: robblau

shotgun_api3/shotgun.py

@@ -1848,7 +1848,7 @@ def _parse_http_status(self, status):
         if status[0] >= 300:
             headers = "HTTP error from server"
             if status[0] == 503:
-                errmsg = "Shotgun is currently down for maintenance. Please try again later."
+                errmsg = "Shotgun is currently down for maintenance or too busy to reply. Please try again later."
             raise ProtocolError(self.config.server,
                                 error_code,
                                 errmsg,