INT 33,19 - Get User Alternate Interrupt Address

	AX = 19h
	CX = user interrupt call mask (see below)


	on return:
	BX:DX = user interrupt vector
	CX = user interrupt call mask or zero if not found

		|F-8|7|6|5|4|3|2|1|0| user interrupt mask in CX
		  |  | | | | | | | `--- alt key pressed during event
		  |  | | | | | | `---- ctrl key pressed during event
		  |  | | | | | `----- shift key pressed during event
		  |  | | | | `------ right button up event
		  |  | | | `------- right button down event
		  |  | | `-------- left button up event
		  |  | `--------- left button down event
		  |  `---------- cursor moved
		  `------------ unused

	- returns vector to function defined by INT 33,18
	- searches the event handlers defined by INT 33,18 for a routine
	  with a call mask matching CX