* cygthread.h (cygthread::stack_ptr): New element.

* cygthread.h (cygthread::stack_ptr): New element.
(cygthread::detach): Accept a "wait_for_signal" argument.
(cygthread::terminate_thread): New function.
* cygthread.cc (cygthread::stub): Set stack pointer argument.
(cygthread::terminate_thread): New function.  Forcibly terminate thread.
(cygthread::detach): Optionally wait for signals and kill thread when signal
arrives.
* exceptions.cc (signal_exit): Set signal_arrived prior to exiting to wake up
anything blocking on signals.
* fhandler.h (fhandler_base::set_r_no_interrupt): Change to accept bool
argument.
(fhandler_pipe::ready_for_read): Declare.
* pipe.cc (pipeargs): New structure.
(read_pipe): New thread stub wrapper for normal pipe read.
(fhandler_pipe::read): Modify to call reader in a cygthread, terminating on
signal, as appropriate.
* select.cc (fhandler_pipe::ready_for_read): Define new function.