Include wx/log.h according to precompiled headers of wx/wx.h (with other minor cleaning).

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@38920 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/xrc/xh_treebk.cpp

@@ -19,9 +19,12 @@
 
 #include "wx/xrc/xh_treebk.h"
 
+#ifndef WX_PRECOMP
+    #include "wx/log.h"
+#endif
+
 #include "wx/treebook.h"
 #include "wx/imaglist.h"
-#include "wx/log.h"
 
 IMPLEMENT_DYNAMIC_CLASS(wxTreebookXmlHandler, wxXmlResourceHandler)