Add initial-repeat-time option to allow the first repeat time to be

increased and later reduced, from David le Blanc in GitHub issue 4164.

tmux.h

@@ -1909,6 +1909,7 @@ struct client {
 	char			*exit_message;
 
 	struct key_table	*keytable;
+	key_code		 last_key;
 
 	uint64_t		 redraw_panes;