Cleanup thread handling to resolve non-exiting daemons on FreeBSD.

Cleanup thread handling to resolve non-exiting daemons on FreeBSD.
Seems that calling pthread_exit() in the main (and only active)
thread does not cause the whole process to exit.  Very odd.
Anyways, as we want to whole process to exit, we should just exit
after joining with our other threads.
I've also removed dead code for detaching threads we join with.