HTTPCORE-363: Unnecessary call to isOpen() before calling close

HTTPCORE-358: I/O reactor listener backlog parameter
Contributed by Dmitry Potapov <potapov.d at gmail.com>

HTTPCORE-357: avoid DNS lookup in SSLIOSession in client mode


git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpcore/trunk@1560947 13f79535-47bb-0310-9956-ffa450edef68