Fixed race condition in #shouldExecuteMultipleCallsAndCallback test case

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpclient/trunk@1463521 13f79535-47bb-0310-9956-ffa450edef68
HTTPCLIENT-1213: Avoid parsing HttpCacheEntry date attribute multiple times.
Contributed by Sam Perman <sam at permans.com>

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpclient/trunk@1463551 13f79535-47bb-0310-9956-ffa450edef68