Make fivestar_views_value_text_handler() obey Views "Round" field option

The handler: fivestar_views_value_text_handler(), labeled "Fivestar Stars (text star count)", hardcodes a rounding function into the value. For statistical analysis purposes, it would be better if the value was a true float, and the user could specify the rounding precision in the View. Fortunately, Views 2 has that functionality, so here's a patch that utilizes it for this handler.