Modified queue and stack tests.
Removed explicit casting of values returned by dequeue, peek, top and
pop.
 Changes to be committed:
	modified:   queues/queue.c
	modified:   stack/stack.c
Renamed queue functions to avoid name conflicts.

All function names are now preceded by "queue_".
 Changes to be committed:
	modified:   queues/queue.c
	modified:   queues/queue.h