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

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@39001 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/variant.cpp

@@ -20,6 +20,9 @@
 
 #ifndef WX_PRECOMP
     #include "wx/string.h"
+    #if wxUSE_STREAMS
+        #include "wx/stream.h"
+    #endif
 #endif
 
 #if wxUSE_STD_IOSTREAM
@@ -36,8 +39,7 @@ using namespace std ;
 #endif
 
 #if wxUSE_STREAMS
-#include "wx/stream.h"
-#include "wx/txtstrm.h"
+    #include "wx/txtstrm.h"
 #endif
 
 #include "wx/string.h"