CS444 hw5  Extensions to hw3's Multitasking Kernel
30 pts, due Mon., Dec 11.

There are two options here, A and B.  Choose one and work in
your cs444/hw5 dir.  Provide a README with guide to your sources.
Although you implement only one, you should understand both.
It's best to work in partnerships with one person doing A, the other
B, and consulting on the other one.  Note your partner in README.

Solutions will be provided.

Option A: Preemptive scheduler.

Convert the scheduler to be preemptive, and let process 0 run an
idle loop at normal process level, preempted as necessary for the
user processes.  Of course this requires a clock ticking. 
See sched.txt for more information.

Option B: Semaphore system calls
Implement the simplified semaphore syscall service that Tanenbaum
uses, except with an explicit sem_create:

	semid = sem_create(init_count)
	down(semid)
	up(semid)
	sem_delete(semid)

See sem.txt for more information.

If you would rather try something else, propose it.  However, you'll
still need to understand A and B for the final.