int int86x( int intr_num, union REGS *inregs,
			 union REGS *outregs, struct SREGS *segregs )


	- prototype in dos.h

	- Executes 8086 software interrupt specified by intr_num
	- Copies register values from inregs into the registers
	- also copies segregs->x.ds and segregs->y.es into DS/ES
	- if CF is set, an error has occurred
	- preserves SP register so calls to INT 25 and INT 26 via this
	  function don't require a stack adjustment
	- unique to DOS
	- see	int86()  intdos()	 intdosx()   intr()  REGS