Issue 978: Raw JSON creates vulnerability. Needs wrapping

From http://code.google.com/p/google-caja/issues/detail?id=978
    Our newly provided safe JSON library is JSON safe but not Caja
    safe. If the JSON string to be parsed includes property names that
    end in double underscore, JSON will (correctly, by the JSON spec)
    unparse it.

A temporary solution that filters out disallowed property names.

Longer term solutions that work better with builtin JSON parsers are
discussed in the bug.

Reviewed in the issue and submitted @3282

[MarkM, 2009-02-20 23:30:27]

LGTM