checkpoint/restart

[Kip Macy]

Well the upcall mechanism mostly works, I've updated
the #ifdefs and added some simple test code for it.
http://www.fsmware.com/ckpt5.tgz

However, it appears that the upcalls are messing up the
stack somehow. Instead of checkpoint returning the number
of bytes written, it returns a value less than zero and
sets errno to 210 (the syscall index for checkpoint).
It appears the stack isn't being popped enough.

I'd appreciate it if someone could take a look at the upcall
function (taken from sendsig).

Since I'm effectively sending a signal from a syscall should
I be setting the stack frame pointer to somewhere other than
regs->tf_esp - 1?

			-Kip