implement "--More--" for Qt

Support MSGTYPE=stop by having qt_display_nhwindow(WIN_MESSAGE,TRUE)
issue a tty-style --More-- prompt.  For popup_dialog Off, the prompt
gets appended to the most recent message; for popup_dialog On, it is
issued via a popup and not displayed in the message window.

It accepts <space>, ^J, ^M, and ^[ (ESC) to dismiss.  There's no way
to dismiss it with the mouse (for !popup_dialog) which might need
some fix....

Several adventures along the way.  The '^C-in-parent-terminal triggers
infinite loop repeatedly complaining about "event loop already running"'
is now a one-shot complaint.  It isn't fixed but the severity of
having it happen is greatly reduced.

win/Qt/qt_bind.h

@@ -71,6 +71,7 @@ public:
 	static int qt_nh_poskey(int *x, int *y, int *mod);
 	static void qt_nhbell();
 	static int qt_doprev_message();
+        static char qt_more();
         static char qt_yn_function(const char *question,
                                    const char *choices, CHAR_P def);
 	static void qt_getlin(const char *prompt, char *line);