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 some checks to lumiera_threadpool_release_thread(), maybe too much
modified thread_loop() to return a known value - 0
added checks to lumiera_thread_new()
added a check to lumiera_thread_destroy()
made lumiera_thread_destroy() unlink the thread from a pool list
updated test case to match new debug messages
