Variants should compare as equal

Variants should compare as equal

We need to implement an object comparison callback to ensure
that two variants with identical values (although different JS
objects) compare as equal.

We also add a v8 autotest for this callback.

Change-Id: Idd1ab602d31b398a937d4df4a7bd091aa205de24
Reviewed-on: http://codereview.qt.nokia.com/989
Reviewed-by: Aaron Kennedy <aaron.kennedy@nokia.com>