MSC: void far _setcliprgn( short x1, short y1, short x2, short y2 )

	- prototype in graph.h

	- all graphics output to the screen is limited to the specified
	  region;  output to areas other than this area is clipped
	- (x1,y1) upper left corner of clipping region
	- (x1,y1) lower right corner of clipping region