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

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@38885 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/variant.cpp

@@ -16,6 +16,12 @@
     #pragma hdrstop
 #endif
 
+#include "wx/variant.h"
+
+#ifndef WX_PRECOMP
+    #include "wx/string.h"
+#endif
+
 #if wxUSE_STD_IOSTREAM
     #if wxUSE_IOSTREAMH
         #include <fstream.h>
@@ -38,8 +44,6 @@ using namespace std ;
 #include "wx/tokenzr.h"
 #include "wx/math.h"
 
-#include "wx/variant.h"
-
 IMPLEMENT_ABSTRACT_CLASS(wxVariantData, wxObject)
 
 wxVariant WXDLLIMPEXP_BASE wxNullVariant;