INT 10 - VIDEO - ALTERNATE FUNCTION SELECT (PS,EGA,VGA,MCGA) - ALTERNATE PRTSC

	AH = 12h
	BL = 20h  select alternate print screen routine
Return: nothing
Desc:	installs a PrtSc routine from the video card's BIOS to replace the
	  default PrtSc handler from the ROM BIOS, which usually does not
	  understand screen heights other than 25 lines
Note:	some adapters disable print-screen instead of enhancing it
SeeAlso: INT 05"PRINT SCREEN"