adds a state to each threadpool which can be only offline or online.
One can not acquire new threads when the pool is offline.
no need for waits in the teststuite anymore.
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()
