INT 15 - DESQview v2.20+ - "ASSERTMAP" - GET/SET MAPPING CONTEXT
	AX = 1117h
	BX = 0000h	get current mapping context without setting
	     nonzero	set new mapping context
Return: BX = mapping context in effect before call
	interrupts enabled
Notes:	this function differs from AX = DE17h for DESQview v2.20 through 2.25
	mapping contexts determine conventional-memory addressability; setting
	  a mapping context ensures that the associated program and data areas
	  are in memory for access.  Usable by drivers, TSRs and shared
	  programs.
	caller need not be running under DESQview, but must ensure that the
	  stack in use will not be mapped out by the call
SeeAlso: AX=DE17h,INT 2F/AX=1685h