HTTPCLIENT-1540: Support delegated credentials (ISC_REQ_DELEGATE) via ClientWinAuth
Contributed by Ka-Lok Fung <ka-lok.fung at sap.com>

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpclient/trunk@1618165 13f79535-47bb-0310-9956-ffa450edef68