Copy 1.5.7 and 1.6 info from 1.x branch.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/pool/trunk@1538413 13f79535-47bb-0310-9956-ffa450edef68
Remove duplicate section

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/pool/trunk@1538414 13f79535-47bb-0310-9956-ffa450edef68