Fixed a regression introduced by HTTPCLIENT-1545

* Initially a SEC_E_DOWNGRADE_DETECTED was thrown but this one is not available on Windows XP and tests never pass. Rather use SEC_E_TARGET_UNKNOWN.
* Hostnames must be in lower case when a SPN is provided

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpclient/trunk@1639679 13f79535-47bb-0310-9956-ffa450edef68
HTTPCLIENT-1575: HttpRoute constructor to resolve default target port (-1) based on standard scheme port convention (http -> 80, https -> 443); to be removed in 5.0

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpclient/trunk@1639698 13f79535-47bb-0310-9956-ffa450edef68
HTTPCLIENT-1567: Update SPNEGO scheme name to 'Negotiate'

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpclient/trunk@1639771 13f79535-47bb-0310-9956-ffa450edef68
HTTPCLIENT-1568: Improve docs on AuthSchemes

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpclient/trunk@1639776 13f79535-47bb-0310-9956-ffa450edef68
HTTPCLIENT-1571: Commit for HTTPCLIENT-1562 broke change from HTTPCLIENT-1560

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpclient/trunk@1639784 13f79535-47bb-0310-9956-ffa450edef68
HTTPCLIENT-1567: Update SPNEGO scheme name to 'Negotiate'

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpclient/trunk@1639801 13f79535-47bb-0310-9956-ffa450edef68