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

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@38945 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/gtk1/bitmap.cpp

@@ -11,12 +11,16 @@
 #include "wx/wxprec.h"
 
 #include "wx/bitmap.h"
+
+#ifndef WX_PRECOMP
+    #include "wx/app.h"
+#endif // WX_PRECOMP
+
 #include "wx/palette.h"
 #include "wx/icon.h"
 #include "wx/filefn.h"
 #include "wx/image.h"
 #include "wx/dcmemory.h"
-#include "wx/app.h"
 
 #include <gdk/gdk.h>
 #include <gtk/gtk.h>