Various corrections to jQuery 1.9 externs

- Loosens type of jQuery.each callback's first parameter; common subtype `?` preferred over `(string|number)`.
- Deprecates jQuery.support (see jquery/api.jquery.com#454).
- Adds other possible return values to jQuery.parseJSON (see jquery/api.jquery.com#492).
- 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.

Resolves google/closure-compiler#694.
I considered that, but we really want the union type `(function(number,?)|function(string,?))` (which the compiler would over simplify to `!Function`), since the function passed won't necessarily accept both types. See the API: https://api.jquery.com/jquery.each/