INT 2F - DOS 3.0+ internal - FLUSH BUFFER

	AX = 1215h
	DS:DI -> disk buffer
	SS = DOS DS (must be using a DOS internal stack)
	STACK: WORD drives for which to skip buffer
		ignore buffer if drive same as high byte, or bytes differ and
		  the buffer is for a drive OTHER than that given in low byte
Return: STACK unchanged
Note:	can be called only from within DOS
SeeAlso: AX=1209h