TC: void intr( int intr_num, struct REGPACK *preg )

	- prototype in dos.h

	- same as int86() except that preg contains registers values
	  both before & after executing interrupt
	- preserves SP register so calls to INT 25 and INT 26 via this
	  function don't require a stack adjustment
	- see  int86x()  intdos()  intdosx()   REGS