Explicitly include wx/aui/dockart.h from the file needing it.

src/aui/tabmdi.cpp needs wxAuiDockArt declaration as it uses it, don't rely on
wx/aui/dockart.h being included from other wxAUI headers and include it from
here explicitly.

See #14098.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@71000 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/aui/tabmdi.cpp

@@ -38,6 +38,7 @@
 #endif //WX_PRECOMP
 
 #include "wx/stockitem.h"
+#include "wx/aui/dockart.h"
 
 enum MDI_MENU_ID
 {