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/python_plugin.c

@@ -168,6 +168,8 @@ struct uwsgi_option uwsgi_python_options[] = {
 	{"py-sharedarea", required_argument, 0, "create a sharedarea from a python bytearray object of the specified size", uwsgi_opt_add_string_list, &up.sharedarea, 0},
 #endif
 
+	{"py-call-osafterfork", no_argument, 0, "enable child processes running cpython to trap OS signals", uwsgi_opt_true, &up.call_osafterfork, 0},
+
 	{0, 0, 0, 0, 0, 0, 0},
 };
 
@@ -377,6 +379,11 @@ void uwsgi_python_post_fork() {
 		UWSGI_GET_GIL
 	}	
 
+	// reset python signal flags so child processes can trap signals
+	if (up.call_osafterfork) {
+		PyOS_AfterFork();
+	}
+
 	uwsgi_python_reset_random_seed();
 
 	// call the post_fork_hook