INT 2A CU - PRINT - BEGIN BACKGROUND PRINTING                                   
	AX = 8700h
	CF clear
Return: CF clear if OK to print in background now
	CF set if background printing not allowed at this time
Desc:	used to inform interested programs that PRINT is about to start its
	  background processing, and allow those programs to postpone the
	  processing if necessary
Notes:	when PRINT gains control and wants to begin printing, it calls this
	  function.  If CF is clear on return, PRINT begins its background
	  processing, and calls AX=8701h when it is done.  If CF is set on
	  return, PRINT will relinquish control immediately, and will not
	  call AX=8701h
	PCVENUS (an early network shell by IBMInternational Busiuness MachinesInternational Busiuness Machines) A hardware, software and other service technology company founded in 1911. and CMU) hooks this call to
	  prevent background printing while its own code is active
SeeAlso: AH=80h,AH=81h,AX=8701h