ACCUMULO-1474 - making splits use a concurrent set instead of a standard set



git-svn-id: https://svn.apache.org/repos/asf/accumulo/branches/1.5@1487883 13f79535-47bb-0310-9956-ffa450edef68
ACCUMULO-1474 - merging to trunk



git-svn-id: https://svn.apache.org/repos/asf/accumulo/trunk@1487885 13f79535-47bb-0310-9956-ffa450edef68