Set a watch for immediate handoff of work.

Currently, ordasity will schedule both the node handing off the work
unit and the new node accepting the work unit with a delay, after which
the new node will attempt to claim the work unit by creating an
ephemeral node in ZK. There is a slight race condition here, so often
times the handoff is delayed by a fixed delay time (of 2s) before the
node can be claimed.

This behavior has been modified to use a ZK watch on the ephemeral node
owned by the node handing off the work unit. When the watch fires, the
new node will more reliably be able to claim the work unit without
triggering the delay.
Address review comments.
Add a ZKUtils.exists() method for safety/consistency with other ZooKeeper interactions.
Do not count work units claimed by the local node but not yet
broadcasted via ZK as unclaimed. Resolves spurious 'not starting twice'
warnings, most commonly observed with work units pegged to a given node.
Update tests to reflect this case.
Merge pull request #21 from pkwarren/handoff_watch

Set a watch for immediate handoff of work. [Nice, Philip!]
[maven-release-plugin] prepare release ordasity-scala_2.9.1-0.5.5
[maven-release-plugin] prepare for next development iteration
ClusterConfig doesn't take arguments, just use setHosts
Merge pull request #23 from tcrayford/fix_readme

ClusterConfig doesn't take arguments, just use setHosts
Update overlock and exclude jline.
[maven-release-plugin] prepare release ordasity-scala_2.9.1-0.5.6
[maven-release-plugin] prepare for next development iteration
Initialize load map to prevent NPE.
[maven-release-plugin] prepare release ordasity-scala_2.9.1-0.5.7
[maven-release-plugin] prepare for next development iteration
Switch to using upstream Twitter ZK client.

Now that the upstream client has the Listener interface added, switch to
it instead of the Boundary fork.
Merge pull request #26 from pkwarren/upstream_twitter

Switch to using upstream Twitter ZK client.
Clean up tasks in shutdown hook.

When the shutdown hook is called, perform a clean shutdown of services
to allow cluster listeners to be called appropriately instead of simply
removing the ephemeral node in ZK.
Merge pull request #27 from pkwarren/cleaner_shutdown

Clean up tasks in shutdown hook.
[maven-release-plugin] prepare release ordasity-scala_2.9.1-0.5.8