intype_callback_init

	index.i2.v = intype_callback_init(callback.f.v [,priority.i1.v]
					  [,handle.i1a.r])

	This function will register the routine "callback" with intype.
	Each time INTYPE is called it will call the routine "callback"
	before returning to intypes caller.

	callback	address of a routine which will be called as follows
			each time intype is called:

			callback(type.i2.r, row.i2.r, column.i2.r)
		 
			If "callback" modifies any of the arguments the
			modified arguments will be returned to intypes
			caller.
	[priority]	optional callback priority  (If multiple callback
			routines have been registered, routines with higher
			priority are called first.)  (default priority is zero)
	[handle]	null terminated handle string for identification
			purposes (default is NULL)

	This function returns status values as follows:

	index		intype registration index which may be used to 
			remove the callback registration by calling the 
			intype_callback_term routine.
	   -1		No room in the callback list.

	This function requires the following include files:

	clib_h

	Related functions:

	intype_callback_term, intype

	C/C++ usage:

	char	priority = 0;
	static const char	handle[] = "my callback";
	short	index;
	void	callback(short *type, short *row, short *column);

	index = intype_callback_init(callback,priority,handle);