(writepipe_exists): New class element.
(orig_pid): Ditto.
(id): Ditto.
(is_slow): Eliminate.
* pipe.cc (fhandler_pipe::set_close_on_exec): Set inheritance on
writepipe_exists, if it exists.
(fhandler_pipe::hit_eof): New method, modelled after tty.
(fhandler_pipe::dup): Duplicate writepipe_exists, if it exists.
(make_pipe): Set up a dummy event for pipes on windows 9x. The nonexistence
of this event means that the write side of the pipe has closed.
(_dup): Move to syscalls.cc
(_dup2): Ditto.
* dtable.cc (dtable::build_fhandler): Fill out set_names here, if appropriate.
* syscalls.cc (_open): Call set_names in build_fhandler.
