Add check for wxUSE_EXTENDED_RTTI to the xti sample header

The sample requires wxUSE_EXTENDED_RTTI to be enabled, and that is correctly signalled
in the source files. Just avoid the header flooding the output with errors.

Closes https://github.com/wxWidgets/wxWidgets/pull/525

* Removed BOM.

samples/xti/codereadercallback.h

@@ -11,6 +11,8 @@
 #ifndef _CODEDEPERSISTER_
 #define _CODEDEPERSISTER_
 
+#if wxUSE_EXTENDED_RTTI
+
 #include "wx/defs.h"
 #include "wx/sstream.h"
 
@@ -104,4 +106,6 @@ public:
     wxString ValueAsCode( const wxAny &param );
 };
 
+#endif // wxUSE_EXTENDED_RTTI
+
 #endif