Fix the case when emacsclient is run on Emacs's controlling tty.

Fix the case when emacsclient is run on Emacs's controlling tty.

src/term.c (O_NOCTTY): Make sure it's defined.
(no_controlling_tty): New variable.
(init_initial_display, mark_ttys): Remove unused variable.
(term_init): Check that the given filename is a terminal device.
Dissociate the controlling terminal if we reopen it for other purposes.
(Reported by Dan Nicolaescu <dann at ics dot uci dot edu>.
(Fdelete_tty): Return nil.

git-archimport-id: lorentey@elte.hu--2004/emacs--multi-tty--0--patch-72