Made all cookie spec implementations thread safe

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpclient/trunk@1620612 13f79535-47bb-0310-9956-ffa450edef68
Default cookie spec to permit 'expires' attribute for Netscape style cookies only

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpclient/trunk@1620613 13f79535-47bb-0310-9956-ffa450edef68
Cookie spec provides to re-use the same thread-safe CookieSpec instance by default

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpclient/trunk@1620787 13f79535-47bb-0310-9956-ffa450edef68