Move single-include guards inside include guards

gcc has optimizations for include guards that only work
if they are outermost in the the header.
https://bugzilla.gnome.org/show_bug.cgi?id=689810

gtk/gtkaccelmapprivate.h

@@ -15,14 +15,14 @@
  * License along with this library. If not, see <http://www.gnu.org/licenses/>.
  */
 
-#if !defined (__GTK_H_INSIDE__) && !defined (GTK_COMPILATION)
-#error "Only <gtk/gtk.h> can be included directly."
-#endif
-
 #ifndef __GTK_ACCEL_MAP_PRIVATE_H__
 #define __GTK_ACCEL_MAP_PRIVATE_H__
 
 
+#if !defined (__GTK_H_INSIDE__) && !defined (GTK_COMPILATION)
+#error "Only <gtk/gtk.h> can be included directly."
+#endif
+
 #include <gtk/gtkaccelmap.h>
 
 G_BEGIN_DECLS