INT 2F - MS Windows 3+ - BEGIN CRITICAL SECTION

	AX = 1681h
Notes:	used to prevent a task switch from occurring
	should be followed by an INT 2F/AX=1682h call as soon as possible
	nested calls are allowed, and must be followed by an appropriate number
	  of "end critical section" calls
	not supported in Windows/386 2.x. Get INDOS flag with INT 21/AH=34h and
	  increment by hand.
SeeAlso: AX=1682h,INT 15/AX=101Bh,INT 21/AH=34h