Support for graceful reload of mule processes.

- On reload master now signals mule with HUP instead of KILL.
- Added optional call to PyOS_AfterFork to enable cpython child
  processes to override and trap HUP signal.
- Copied cursed_at/no_mercy_at pattern used with worker processes.
- Added mule_reload_mercy option.

plugins/python/uwsgi_python.h

@@ -197,6 +197,8 @@ struct uwsgi_python {
 	PyObject *raw_callable;
 
 	struct uwsgi_string_list *sharedarea;
+
+	int call_osafterfork;
 };