disable text% offscreen buffer for OS X in an effort to improve anti-aliased onscreen text

svn: r7729

src/mred/wxme/wx_mbuf.cxx

@@ -465,6 +465,10 @@ Bool wxMediaBuffer::ReadyOffscreen(double width, double height)
       || (height > REDICULOUS_SIZE))
     return FALSE;
 
+#ifdef wx_mac
+  return FALSE;
+#endif
+
   if (!offscreenInUse && (height > bmHeight || width > bmWidth)) {
     wxBitmap *oldbm = bitmap;