[2.3.x] Fix for https://java.net/jira/browse/GRIZZLY-1532 (IdleTimeoutFilter worker implementation should only perform work on open connections)
+ return GrizzlyFuture for consistency
+ checkpoint for
issue #1527
https://java.net/jira/browse/GRIZZLY-1527

"Implement client-side Connection pool"
[2.3.x] + add javadoc
[2.3.x] + fix connection-pool bug: initiate connect after updating asyncWaitingList