Disable some Audio_Region context menu items when appropriate.

Timeline/Audio_Region.C

@@ -312,9 +312,9 @@ Audio_Region::menu ( void )
             { "Fade in to mouse", FL_F + 3, 0, 0 },
             { "Fade out to mouse", FL_F + 4, 0, 0 },
             { "Loop point to mouse", 'l', 0, 0 },
-            { "Clear loop point", FL_SHIFT + 'l', 0, 0 },
+            { "Clear loop point", FL_SHIFT + 'l', 0, 0, 0 == _loop ? FL_MENU_INACTIVE : 0 },
             { "Normalize", 'n', 0, 0 },
-            { "Denormalize", FL_SHIFT + 'n', 0, 0 },
+            { "Denormalize", FL_SHIFT + 'n', 0, 0, 1.0 == _scale ? FL_MENU_INACTIVE : 0 },
             { "Range from", FL_CTRL + 'r', 0, 0 },
             { "Remove", 0, 0, 0 },
             { 0 },