Change list(String groupName) method to be private, since it really cannot
be called independently due to its interaction with the semaphore.
Merge branch 'master' of github.com:sleberknight/zookeeper-samples
Add GroupMembershipIterable example.

This is a class that implements Iterable<List<String>> to watch a znode for changes to
 children and return a List<String> from next(). The hasNext() initially returns true if the
 znode exists, and thereafter blocks until changes are made to the znode, e.g. until it is
 either deleted or if children are added/removed.