Page Comparison

IN:
     IX = stream handle	-

OUT, if call successful:
     Fc = 0, input MAY BE available
	 A = input source
		  XIN_KB ($01), keyboard buffer has data, possibly ESC or pre-emption
		  XIN_RX ($02), serial RX buffer has data
     	  XIN_CLI ($04), CLI is active
OUT, if call failed:
     Fc = 1
     A = error code:
          RC_EOF ($09), OS_In will not return immediately if called
          RC_HAND ($08), bad handle

Registers changed after return:
     ..BCDEHL/IXIY same
     AF....../.... different