core: compile fix with namespaces

Change-Id: Ibbf2711d7d7ce2b0ec56c93bb0ceac3dfa785756
Reviewed-on: http://codereview.qt.nokia.com/3106
Reviewed-by: hjk <qthjk@ovi.com>

src/plugins/coreplugin/fileutils.h

@@ -35,10 +35,11 @@
 
 #include "coreplugin/core_global.h"
 
+QT_BEGIN_NAMESPACE
 class QWidget;
+QT_END_NAMESPACE
 
 namespace Core {
-
 namespace Internal {
 
 struct CORE_EXPORT FileUtils