FIXED #11. added factory option in slacker-cluster function.

(which is already implemented :)
FIXED #9. Added support for custom merge function.
WIP #14. Added zookeeper base functions backed by Curator
WIP #14. Added more implement to keep interfaces unchanged in zookeeper module.
minor tweak
Implement new zk interfaces in client API. Fixed #14.
bring back slf4j-log4j
also bring back log4j, fixed test initialization error
Only process zk node events
update curator
update project.clj
Merge branch '0.12-dev'

Conflicts:
	project.clj
	src/slacker/client/cluster.clj
bump version and release rc1