moved wx/panel include to correct wxGTK compilation error

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@12688 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

samples/widgets/widgets.cpp

@@ -28,7 +28,6 @@
 #ifndef WX_PRECOMP
     #include "wx/app.h"
     #include "wx/log.h"
-    #include "wx/panel.h"
     #include "wx/frame.h"
     #include "wx/button.h"
     #include "wx/checkbox.h"

samples/widgets/widgets.h

@@ -19,6 +19,8 @@ class WXDLLEXPORT wxTextCtrl;
 
 class WXDLLEXPORT WidgetsPageInfo;
 
+#include "wx/panel.h"
+
 // all source files use wxImageList
 #include "wx/imaglist.h"