MSC: void _chain_intr( void (interrupt far *target)() )

	- prototype in dos.h

	- chains from one interrupt handler to another;  sets up the
	  stack as if the interrupt was called directly by pushing the
	  flags and the original return address on the stack
	- this function does not return to caller but returns to the
	  code where the interrupt occurred
	- no corresponding function in Turbo C