use ctrl_nhwindow() for menu prompt style

This implements the mechanics to use the ctrl_nhwindow() interface
capability to pass down a setting change from the core to the active
window port, without resorting to accessing a core global variable
from within the window port, and without altering the interface..

The passed setting is honored in the tty and curses window ports.

X11 and mswin receive and store the values, but no implementation
to change the menu prompt style is there yet.

Qt does not store the values or have an implementation.

The setting change is done in allmain.c immediately after
creating the WIN_INVEN window.

include/flag.h

@@ -186,10 +186,6 @@ struct debug_flags {
 #endif
 };
 
-typedef struct color_and_attr {
-    int color, attr;
-} color_attr;
-
 /*
  * Stuff that really isn't option or platform related and does not
  * get saved and restored.  They are set and cleared during the game