* cygthread.cc (cygthread::stub): Set inuse to false when exiting.

* cygthread.cc (cygthread::stub): Set inuse to false when exiting.
(cygthread::cygthread): Actually pass name as argument to debugging output to
avoid SEGV when strace'ing.
(cygthread::release): Don't set stack_ptr to NULL, since it is only set once on
first entry to a stub not on each stub iteration.
(cygthead::exit_thread): Remove obsolete function.
* cygthread.h (cygthread::exit_thread): Ditto.