pc/i8259.c		1997/0327		Created.
		1997/0521		format edit
		1998/0320		add print for out-of-range vectors
		1998/0910		XXX bug fix?: add i8259lock. Change Vector* to Irq*.
		1998/1022		hw BUG fix? better test for edge/level register. publish elcr
		1998/1114		set int1mask (BUG fix?)
		1999/0301		replace int0mask, int1mask with i8259mask. replace elcr with i8259elcr. check for shared non-level-triggered interrupts.
		1999/0714		Use ioalloc.
		2001/0222		add i8259dump
		2001/0428		remove i8259dump
		2001/0527		enable ELCR print
		2001/0905		add i8259disable, i8259vecno (new arch code? XXX)