HTTPCLIENT-1458: SystemDefaultCredentialsProvider always uses 'http' as an authentication protocol to Authenticator#requestPasswordAuthentication call

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpclient/branches/4.3.x@1567927 13f79535-47bb-0310-9956-ffa450edef68
Unused import

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpclient/branches/4.3.x@1567932 13f79535-47bb-0310-9956-ffa450edef68
Use AtomicBoolean to hold storage status

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpclient/branches/4.3.x@1567936 13f79535-47bb-0310-9956-ffa450edef68