======register_callback======
WM-MEGA, WM-M2, WM-MINI2 >= 2.1000
Register a call back to a system event
====Description====
int
register_callback (
string
$callback_type
[,
int
$script_name
]
[,
string
$function_name
] )
This function will register a callback which will be called when a system event occurs.