* fhandler_tty.cc (fhandler_tty_common::dup): Just copy cygheap->ctty to child

* fhandler_tty.cc (fhandler_tty_common::dup): Just copy cygheap->ctty to child
if duping the current ctty.
(fhandler_tty_common::close): Move debugging statement earlier in function.
(fhandler_tty_slave::close): Return success when closing ctty.
* syscalls.cc (close_all_files): Avoid calling fhandler_tty_slave close method
so that open_fhs will not be decremented when closing cygheap ctty.
(setsid): Ditto.
* dcrt0.cc (do_exit): Reorganize to avoid leaving a critical section active
after vfork.
* fhandler.h (fhandler_tty_slave::get_unit): Remove regparm parameter since it
can't work in a virtualized function.