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

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@39247 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/gtk/bitmap.cpp

@@ -10,13 +10,14 @@
 // For compilers that support precompilation, includes "wx.h".
 #include "wx/wxprec.h"
 
+#include "wx/bitmap.h"
+
 #ifndef WX_PRECOMP
     #include "wx/app.h"
     #include "wx/dcmemory.h"
+    #include "wx/palette.h"
 #endif
 
-#include "wx/bitmap.h"
-#include "wx/palette.h"
 #include "wx/icon.h"
 #include "wx/filefn.h"
 #include "wx/image.h"