Update select2.js, fixes #781

As suggested in https://github.com/ivaynberg/select2/issues/781#issuecomment-38979100, significantly improves search speed, going from unusable to snappy on IE on a list of almost 10,000 items with a custom query limiting it to 25 results. Uses 'uni range + named function' from http://jsperf.com/diacritics/18