JENA-638 : Rewrite TransformTopN to treate more generally.
Add TestTransformTopN for this specific transform.
Refactor tests to out optimizer/transforms in their own TS_Optimization.

git-svn-id: https://svn.apache.org/repos/asf/jena/trunk@1568664 13f79535-47bb-0310-9956-ffa450edef68