A better function to filter valid Friendly URL.

I am having problems in a project because sometimes the first sentence in the input has special characters. For example. in Spanish, the symbol " ¿ " is used to open a question. This characters have been validated in the friendly URL, but they shouldn't, because this type of symbol sends you to a 404 error page. 

I've changed the code to reuse an internal function in Tools.php to filter a string to be a valid friendly URL  that accomplish that goal in a more efficient way.