[2.3.x] + additional update for
implement improvement #1524
https://java.net/jira/browse/GRIZZLY-1524
"Investigate possibility of using ListenableFuture-like funtionality in GrizzlyFuture"

use HashSet + synchronize instead of ConcurrentHashMap for less memory consumption
[2.3.x] [2.3.x] + implement + checkpoint for
issue #1527
https://java.net/jira/browse/GRIZZLY-1527
"Implement client-side Connection pool"

Add max reconnect attempts.  Defaults to five.
If reconnect feature is disabled and the pool is unable to connect, async pollers are notified of connection failure.
If reconnect feature is enabled and the pool is unable to connect and if the max number of connect attempts is exceeded, then async pollers will be notified of connection failure.