hw5 Option B: Semaphore system calls
Implement the simplified semaphore syscall service:

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

Make the process block when waiting on a semaphore.  
Use FIFO among the waiting processes, or explain what other
scheme you are using.  The same queue package we used before, 
modified for holding ints instead of chars, is provided in 
subdirectory "intqueue".

There is a challenge here to overcome a mismatch between the
"broadcast" wakeup and the selective action of "up", which is
supposed to awaken only one process.  Each process awakened
on a semaphore needs to check that it is an "appointed" one.
Two ups in quick succession would similarly appoint two
processes.  You can use a new field in PEntry to keep track
of a processes' semaphore-status.

Our system now takes a three user programs in one file, that
is, a trio of user programs.

The user level program trio prodcons.c is supplied, that also uses an
intqueue for the shared buffer between the producer and consumer.
A simpler user test program trio using only mutex is provided in
testmutex.c.

Note the debuglog facility.  You can use this to track events
in your semaphore service without disturbing the timing with
output.  In particular, add little reports such as "up(0:1)"
to mark an up that makes sem 0's count reach 1.

Testing: your scripts should show debuglog output.

1. First get testmutex working.  See testmutex.script.
Make your own testmutex.script.

2. Then get prodcons working.  See prodcons.script. Make your own script 
in prodcons.script.

3. Finally, modify testmutex to have main1 join the group trying
to input from the console one by one under mutex.  Call this testmutex3.c
since it has 3 processes using the mutex.  Make a script in testmutex3.script.