Code cleanups

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpclient/trunk@1571714 13f79535-47bb-0310-9956-ffa450edef68
Made AsynchronousValidationRequest public

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpclient/trunk@1571715 13f79535-47bb-0310-9956-ffa450edef68
Add release 4.3.3 to RN history.

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpclient/trunk@1572167 13f79535-47bb-0310-9956-ffa450edef68
Cleanups in CachingExec and related test classes