* cygthread.cc (cygthread::exit_thread): Define new method.

* cygthread.cc (cygthread::exit_thread): Define new method.
* cygthread.h (cygthread::exit_thread): Declare new method.
* fhandler.h (fhandler_tty_master::hThread): Delete.
(fhandler_tty_master::output_thread): Define.
* fhandler_tty.cc (fhandler_tty_master::fhandler_tty_master): Adjust
constructor.
(fhandler_tty_master::init): Use cygthread rather than handle.
(process_output): Use cygthread method to exit.
(fhandler_tty_master::fixup_after_fork): Set output_thread to NULL after fork.
(fhandler_tty_master::fixup_after_exec): Set output_thread to NULL after
spawn/exec.
* tty.cc (tty_list::terminate): Detach from output_thread using cygthread
method.