Updated pcb and queue.

- There was a bug in the previous pcb version and it's now fixed.
- Queue has been improved. The strong bounding condition has been added back
  into the queue since each pcb stores it's own priority, nodes no longer need
  to worry about the parent level.

  In addition, q_size() is removed as it's not used.

- Also, whenever a fork or malloc fails, an error message is printed and the
  program immediately terminates. Returning NULL or simply leaving the function
  with something like this fails was bad.
Completed exercise 9 labs.

- Fully operational.