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

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@39957 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/gtk/dcclient.cpp

@@ -20,9 +20,9 @@
     #include "wx/log.h"
     #include "wx/dcmemory.h"
     #include "wx/math.h" // for floating-point functions
+    #include "wx/image.h"
 #endif
 
-#include "wx/image.h"
 #include "wx/module.h"
 #include "wx/fontutil.h"