Added code for efficience when a Set is used as the collection

git-svn-id: https://svn.apache.org/repos/asf/jena/trunk@1554630 13f79535-47bb-0310-9956-ffa450edef68
deprecated GraphMemPlain in favore of CollectionGraph
Added correct graph capabilities

git-svn-id: https://svn.apache.org/repos/asf/jena/trunk@1554631 13f79535-47bb-0310-9956-ffa450edef68