JENA-513 , JENA-514 : DatasetGraphBase.deleteAny rewritten to work in slices.

Instead of copying the whole iterator, the code takes slices, and repeats until
the "deleteAny" pattern no longer causes .find to return anything.




git-svn-id: https://svn.apache.org/repos/asf/jena/trunk@1515213 13f79535-47bb-0310-9956-ffa450edef68