INT 2F - European MS-DOS 4.0 POPUP - "PostPu" - OPEN/CLOSE POPUP SCREEN
	AX = 1401h
	DL = function (00h open, 01h close)
	DH = wait flag
	    00h block until screen opens
	    01h return error if screen is not available
	    02h urgent--always open screen immediately
Return: CF clear if successful
	    BX = amount of memory needed to save screen and keyboard info,
		0000h if default save location can be used (only if DH was 02h)
	CF set on error
Note:	the application using the screen is frozen until the popup screen is
	  closed
SeeAlso: AX=1400h"POPUP",AX=1402h"POPUP",AX=1403h"POPUP"