Initial implementation support for a few Leviathan extension functions (JENA-507)

git-svn-id: https://svn.apache.org/repos/asf/jena/trunk@1512416 13f79535-47bb-0310-9956-ffa450edef68
Initial unit tests for Leviathan extension functions (JENA-507)

git-svn-id: https://svn.apache.org/repos/asf/jena/trunk@1512418 13f79535-47bb-0310-9956-ffa450edef68