Various corrections to jQuery 1.9 externs

- Corrects type of jQuery.each callback's first parameter to `(number|string)` instead of `string`.
- Deprecates jQuery.support (see jquery/api.jquery.com#454).
- Adds other possible return values to jQuery.parseJSON (see jquery/api.jquery.com#490).
- Loosens return type of `dataFilter` function passed to $.ajax (see jquery/api.jquery.com#492).
- Updates `@see` reference to link to proper issue in old tracker.