SLING-3241 Unwrapped any wrapped objects before returning
the result from script evaluation.

Also adapted the ScriptableResourceTest becaused "undefined" is returned
as null now. The test evaluates a comparison to the undefined value and
verifies the result is true.

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1541393 13f79535-47bb-0310-9956-ffa450edef68