Non-blocking connection pool to avoid scanning the entire queue of pending connection requests on each connection lease / release operation (under heavy load the request queue can contain a significant number of pending requests, a full linear scan of which can cause massive performance degradation)

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpcore/trunk@1478039 13f79535-47bb-0310-9956-ffa450edef68