Fix of DistributedAtomicValue#compareAndSet to work with empty node

https://issues.apache.org/jira/browse/CURATOR-108

Fix of DistributedAtomicValue#compareAndSet to work with value from node with no data (byte[0]{}). Such value is not equal to correct zero representation of integer (byte[4]{0,0,0,0}) and long (byte[8]{0,0,0,0,0,0,0,0}) in terms of Arrays.equals.