INT 15 - DESQview v2.26+ - "ASSERTVIR" - CONTROL 386 SCREEN VIRTUALIZATION
	AX = DE21h
	BX = new state
	    0000h turn off
	    nonzero turn on
Return: BX = old state of virtualization
Notes:	this API(Application Program[ming] Interface) The defined set of calls which a program may make to interact with or request services of the operating system or environment under which it is running.  Because the inputs and outputs of the calls are well-defined, a program using the API can continue using the identical calls even if the internal organization of the program providing the API changes. call may be made from within a hardware interrupt handler
	under DV 2.40 and 2.42, this call appears to have no effect and always
	  returns a nonzero value in BX which appears to be the offset within
	  the DV common memory segment of the caller's task object; it may
	  only have an effect within a hardware interrupt handler
SeeAlso: AX=1117h,AX=DE17h