* cygthread.cc (cygthread::stub): Don't create an event for "cygself" threads.

* cygthread.cc (cygthread::stub): Don't create an event for "cygself" threads.
Assume that they exit via an ExitThread call.
* cygthread.h (cygthread::SetThreadPriority): New function.
(cygthread::zap_h): New function.
* dcrt0.cc (do_exit): Move cygthread::terminate earlier and establish
exit_state guard.
* fhandler.h (fhandler_tty_master::output_thread): Delete.
* fhandler_tty.cc (fhandler_tty_master::init): Set priority for threads via
method.  Zap handles when done.  Don't treat process_output specially.
(process_output): Call ExitThread directly.
(fhandler_tty_master::fixup_after_fork): Don't worry about output_thread.
(fhandler_tty_master::fixup_after_exec): Ditto.
* sigproc.cc (proc_terminate): Don't detach from hwait_subproc.  Just let it
exit.
(sigproc_init): Close thread handle after initialization.
(wait_sig): Use GetCurrentThread() as SetThreadPriority call rather than
*event* handle.  Call ExitThread directly on termination.
(wait_subproc): Call ExitThread directly on termination.
* tty.cc (tty_list::terminate): Don't attempt t detach from output_thread.