add LUMIERA_DIE in cases where this soft limit is reached
add LUMIERA_DIE when pthread_create fails to create threads - serious
add a test which tries to break the soft limit
output the size of the created thread struct
don't print "destroying thread" (lets tests become shorter with repeated matching)
add a test which spans many threads in all pools
added locking and checks to lumiera_threadpool_acquire_thread()
added a nobug flag to threads.c
added lumiera_thread_destroy()
added lumiera_thread_delete()
