Implement BPTree.clear

git-svn-id: https://svn.apache.org/repos/asf/jena/trunk@1607652 13f79535-47bb-0310-9956-ffa450edef68
No need to put DEPENDENCIES in the distribution file

git-svn-id: https://svn.apache.org/repos/asf/jena/trunk@1607653 13f79535-47bb-0310-9956-ffa450edef68