bug fixes

About the yahoo engine : 
- Yahoo returns a specifc page for mobile phone, and the xpath are not the same. (Yahoo use the User-Agent to detect the mobile)
- the url redirection from Yahoo: I have add a hack to the xpath engine to parse yahoo url. It's ugly but it's work.

May be the url_normalize function could help for all engines : 
- it could be use the change all http://*.wikipedia.org to https://*.wikipedia.org (and avoid duplicate results)
- if necessary, fetch real url from url redirection website.
- and replace yahoo redirection.

About xpath engine : with this version, the engine gets the text node from selected path. If there is more than one node, everything in concated. It works also if it's a attribute. 

About locale : I haved added more locale parameter to engines.cfg. May be we could image a mapping between Accepted-Language http header and the locale parameter, or let the user choices what he want.