QPID-5356: stop default search for client certificate when not specified

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1547951 13f79535-47bb-0310-9956-ffa450edef68
QPID-5375: make Windows client certs more like their Posix counterpart, no longer restricted to SASL EXTERNAL

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1547958 13f79535-47bb-0310-9956-ffa450edef68
Merge trunk into messaging-logging