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/gtkinfobar.h

@@ -26,13 +26,13 @@
  * Modified by the GTK+ Team, 2008-2009.
  */
 
+#ifndef __GTK_INFO_BAR_H__
+#define __GTK_INFO_BAR_H__
+
 #if !defined (__GTK_H_INSIDE__) && !defined (GTK_COMPILATION)
 #error "Only <gtk/gtk.h> can be included directly."
 #endif
 
-#ifndef __GTK_INFO_BAR_H__
-#define __GTK_INFO_BAR_H__
-
 #include <gtk/gtkbox.h>
 #include <gtk/gtkenums.h>