Clean up tty device handling. Change name of controlling tty from nil to "/dev/tty".

Clean up tty device handling.  Change name of controlling tty from nil to "/dev/tty".

* src/term.c: Include errno.h.
  (Fcontrolling_tty_p): Compare name with "/dev/tty", not NULL.
  (Fresume_tty): Handle errors on reopening ttys.  Don't
  dissociate if terminal was explicitly opened on the controlling
  terminal.
  (init_tty): Initialize local pointers.  Always set name (use
  "/dev/tty" for controlling tty.)  Remove special case for name == NULL.

git-archimport-id: lorentey@elte.hu--2004/emacs--multi-tty--0--patch-538