Avoid unnecessary window updates

Add a window bitmask to wins_update() and only update windows that might
actually require an update in our main loop. This improves response
times of the user interface a bit.

Signed-off-by: Lukas Fleischer <calcurse@cryptocrack.de>

src/custom.c

@@ -696,8 +696,8 @@ custom_sidebar_config (void)
       else
         {
           wins_reinit_panels ();
-          wins_update_border ();
-          wins_update_panels ();
+          wins_update_border (FLAG_ALL);
+          wins_update_panels (FLAG_ALL);
           keys_display_bindings_bar (win[STA].p, binding, 0, binding_size);
           wins_doupdate ();
         }