This is the new way for working with arguments in JSNative functions.
JS_THIS_VALUE, JS_ARGV, JS_SET_RVAL and direct access to vp or argc are
deprecated and will probably be removed in future versions of
SpiderMonkey.
CallArgs also takes care of proper rooting and you can get the values as
Handles or MutableHandles. The interface changes a little bit for ESR
31, but commiting this now still makes it easier and the changes shout
be straigtforward (search and replace more or less).
Refs #2462
Refs #2415
This was SVN commit r15516.