	The program finds a specified number of prime numbers, then 
	sorts and displays these numbers.  Several threads 
	participate in the search : each thread takes a number ( the 
	next one to be checked), checks if it is a prime, records it 
	if it is a prime, and then takes another number -- and so 
	on.  


	The following pthread routines are used in this example:

		pthread_mutex_init();
		pthread_mutex_lock();
		pthread_mutex_unlock();

		pthread_cond_init();
		pthread_cond_wait();
		pthread_cond_broadcast();

		pthread_setcancel();
		pthread_cancel();
		pthread_testcancel();


		pthread_create();
		pthread_join();
		pthread_detach();
		pthread_exit();
		pthread_yield();
