Apply display::summary_argument() filters in view::get_url()

Currently if an incorrectly formatted argument is sent into Views it gets re-exposed incorrectly by Views even if the arguments has filters to prevent that. Eg. views_handler_argument_string has filters that normalizes the argument values - but they are not called by view::get_url().

I haven't checked what the case is for Views 3, but I'm attaching a working, although a bit hackish, patch for Views 2 that makes view::get_url() use display::summary_argument().

Also - partly related - where is the $arguments variable in view::get_url() coming from? It's accessed in there prior to it being assigned any value?