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

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@39285 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/os2/timer.cpp

@@ -12,6 +12,8 @@
 // For compilers that support precompilation, includes "wx.h".
 #include "wx/wxprec.h"
 
+#include "wx/timer.h"
+
 #ifndef WX_PRECOMP
     #include "wx/list.h"
     #include "wx/window.h"
@@ -23,8 +25,6 @@
 
 #include "wx/os2/private.h"
 
-#include "wx/timer.h"
-
 #include <time.h>
 #include <sys/types.h>