ACCUMULO-1338 fixed issue w/ closeScanner() in proxy

git-svn-id: https://svn.apache.org/repos/asf/accumulo/branches/1.5@1471607 13f79535-47bb-0310-9956-ffa450edef68
ACCUMULO-1340 made proxy update call tolerate unknown session ids

git-svn-id: https://svn.apache.org/repos/asf/accumulo/branches/1.5@1471643 13f79535-47bb-0310-9956-ffa450edef68