Restore comment wrongly removed by c269398.

The comment is (probably) still relevant, otherwise we wouldn't need this code
at all but could just disable the control normally. It was probably removed
because of a mix up between "disabling the control" and "settings its colour
to disabled".

See #10254.

src/osx/cocoa/stattext.mm

@@ -60,8 +60,10 @@
 
     [super setEnabled: flag]; 
     
-    if (![self drawsBackground])
-    { 
+    if (![self drawsBackground]) {
+        // Static text is drawn incorrectly when disabled.
+        // For an explanation, see
+        // http://www.cocoabuilder.com/archive/message/cocoa/2006/7/21/168028
         if (flag)
         { 
             if (m_textColor)