pegbox: add cli/sti, to ensure interrupts disabled whenever a spinlock held
pegasus: make lock debugging work on all pages, not just page 0
pegasus: added 'IRQ primed' latch to interrupt chain

When an interrupt is accepted, blocks further interrupts until the
 interrupt acknowledge cycle completes.  The hardware implementation of
 this will be different, as the Z80 doesn't have an explicit interrupt
 acknowledge line; instead the MMU will have to wait for the rising edge
 of \IORQ, or something.  We'll cross that southbridge when we come to it.
pegbox: scheduler: don't lose percpu stack in do_fork()

When writing SP to MEM_SAVESP (before copying the process image), use an
 SPSWAP so that the percpu-stack SP is preserved.
pegbox: fix return address in timer interrupt handler

When we call sched_enter, it will (eventually) RETurn to the caller.  But
 if we just pre-empted someone (possibly the idle loop), it's them we want
 to return to, not INT_timer.  So JP sched_enter instead of CALLing it,
 ensuring that the return address is the instruction that got interrupted.