* dtable.cc (fh_alloc): Revert ill-advised setting of major/minor. Use new
is_dev_tty to remember that this device was opened as /dev/tty.
* fhandler.cc (fhandler_base::fstat): Remove leftover debugging statement.
(fhandler_base::tcgetsid): New function.
* fhandler.h ((fhandler_base::tcgetsid): Declare new function.
(fhandler_base::is_dev_tty): Ditto.
(fhandler_termios::opened_as_dev_tty): Declare new field.
(fhandler_termios::is_dev_tty): Declare new function.
(fhandler_termios::tcgetsid): Ditto.
(fhandler_pty_common::use_archetype): Move here from subclass.
(fhandler_pty_slave::use_archetype): Move up.
(fhandler_pty_master::use_archetype): Ditto.
* fhandler_console.cc (fhandler_console::ioctl): Rename second argument from
`buf' to `arg' for consistency. Call ioctl_termios for common fhandler_termios
ioctl handling.
* fhandler_tty.cc (fhandler_pty_slave::ioctl): Call ioctl_termios for common
fhandler_termios ioctl handling.
(fhandler_pty_master::ioctl): Ditto.
* fhandler_termios.cc (fhandler_termios::tcgetsid): Implement new function.
(fhandler_termios::ioctl_termios): Ditto. Implements TIOCSCTTY handling.
* syscalls.cc (stat_worker): Set /dev/tty device info when appropriate.
* termios.cc (tcgetpgrp): Avoid extraneous "isatty" check.
(tcgetsid): Implement new function.
* include/cygwin/version.h: Bump CYGWIN_VERSION_API_MINOR to 253.
* include/sys/termios.h (TIOCSCTTY): Define.