Deprecate / remove support for the javascript date format in JSON converter

After upgrading our app to jQuery 1.4.2 which now uses browser's native JSON parsing, we find that the "x":new Date(45749857489) format is actually not legal JSON according to the JSON spec, and jQuery fails to parse this JSON (well the browser fails to, so this will affect other libraries using window.JSON)

In grails we have a setting to allow dates to be specified in this way - we need to deprecate or remove this feature as producing illegal JSON that fails to parse on clients is never going to be a good idea going forward.

More info:

http://www.neeraj.name/blog/articles/895-handling-json-parsing-natively-in-jquery-1-4-and-what-changed-from-jquery-1-3