call GtkWidget's key_press_event callback for keys, in case GtkWidget has

call GtkWidget's key_press_event callback for keys, in case GtkWidget has

* src/vte.c(vte_terminal_key_press): call GtkWidget's key_press_event callback
	for keys, in case GtkWidget has pre-programmed behavior for that key
	(#133878).
* configure.in, gnome-pty-helper/configure.in: quote names of defined functions
	(#133222).
* configure.in: make compilation of gnome-pty-helper actually conditional
	(#133077).
* src/vte.c(vte_terminal_process_incoming): Doh #132610, actually call
	vte_terminal_emit_contents_changed() when the contents change.