Rename example classes to reflect the example.

git-svn-id: https://svn.apache.org/repos/asf/jena/trunk@1529194 13f79535-47bb-0310-9956-ffa450edef68
JENA-553 : Reimplment DatasetGraphAltDefaultGraph

And also force DatasetGraph implementations to provide addGraph/removeGraph.

git-svn-id: https://svn.apache.org/repos/asf/jena/trunk@1529265 13f79535-47bb-0310-9956-ffa450edef68
Merge remote-tracking branch: upstream/trunk