HTTPASYNC-56: Moved code requiring synchronization out of #connectionAllocated

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpasyncclient/trunk@1531674 13f79535-47bb-0310-9956-ffa450edef68
Removed MinimalClientExchangeHandlerImpl in favor of DefaultClientExchangeHandlerImpl; eliminated a great deal of duplicate code

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpasyncclient/trunk@1531675 13f79535-47bb-0310-9956-ffa450edef68
Added connection routing related logs

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpasyncclient/trunk@1531676 13f79535-47bb-0310-9956-ffa450edef68
HTTPASYNC-56: fixed connection leak introduced by r1531544

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpasyncclient/trunk@1531677 13f79535-47bb-0310-9956-ffa450edef68