Fixed #622

ReferenceError: Config is not defined when using connection.changeUser
and changing the charset

Author: rwky

lib/Connection.js

@@ -83,7 +83,7 @@ Connection.prototype.changeUser = function(options, cb){
   }
 
   var charsetNumber = (options.charset)
-    ? Config.getCharsetNumber(options.charset)
+    ? ConnectionConfig.getCharsetNumber(options.charset)
     : this.config.charsetNumber;
 
   var self = this;