gtk: Minimize differences with origin/master.

gtk: Minimize differences with origin/master.

This mainly undeletes the primitives TTY-GET-INTERRUPT-CHARS and
TTY-SET-INTERRUPT-CHARS!.  They will not work correctly after gtkio's
signal forwarder is installed, but that does not seem to be a problem.
Deleting them was not a problem!  They are only undeleted now to
minimize differences between the Gtk branch and origin/master.