* fhandler.h (fhandler_tty_slave::ttyname): Use name from pc since it is

* fhandler.h (fhandler_tty_slave::ttyname): Use name from pc since it is
guaranteed to be accurate.
* fhandler_tty.cc (fhandler_tty_slave::open): Increment open_fhs appropriate
when copying ctty.
(fhandler_tty_slave::close): Remove special case handling for exit_state.  Use
ctty < 0 check instead.
(fhandler_tty_common::close): Set io_handle to NULL after closing.
* syscalls.cc (close_all_files): Specifically close cygheap->ctty, if
appropriate.