Various corrections to jQuery 1.9 externs

- Loosens type of jQuery.each callback's first parameter; common subtype ? preferred to (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.
More precise annotation for `jQuery.each`
Merge pull request #694 from usmonster/694-externs-jquery-support

Various corrections to jQuery 1.9 externs