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

	- prototype in graph.h

	- defines a clipping region like _setcliprgn()
	- sets the logical origin to the upper left corner coordinates
	  specified as parameters
	- (x1,y1) upper left corner of window
	- (x2,y2) lower right corner of window