HTTPCLIENT-1493: Indiscriminate connection checking has been deprecated in favor of conditional connection state validation. Persistent connections are to be re-validated only after a defined period inactivity prior to being leased to the consumer.

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpclient/trunk@1604772 13f79535-47bb-0310-9956-ffa450edef68