Fix more typos in comments and wxFAIL messages

Closes https://github.com/wxWidgets/wxWidgets/pull/270

interface/wx/xrc/xmlres.h

@@ -89,7 +89,7 @@ public:
     void AddHandler(wxXmlResourceHandler* handler);
 
     /**
-       Add a new handler at the begining of the handler list.
+       Add a new handler at the beginning of the handler list.
      */
     void InsertHandler(wxXmlResourceHandler *handler);