HTTPCLIENT-1287: DefaultUserTokenHandler#getUserToken to check if the connection is open prior to retrieving SSLSession.
Contributed by Noah Levitt <nlevitt at gmail.com>

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpclient/trunk@1427541 13f79535-47bb-0310-9956-ffa450edef68