Add xmon command to dump process/task similar to ps(1)

[Douglas Miller]

Request for comments

Add a command to xmon that prints basic task information like
ps(1) but includes the kernel stack pointer for use with 't'
(traceback) command.

Adds a macro to be used to wrap memory access with setjmp code
to protect against memory faults.

Is additional locking required? Any other concerns?

Thanks,
Doug