KV-store API changes should be backward compatible to 0.10

SAMZA-813 introduced new methods in KeyValueStore and KeyValueIterator interface classes, which in JDK7, breaks the backward compatibility for customized implementation of KeyValueStore and KeyValueIterator.

As 0.10.1 is a bug-fix release, we should make sure that the backward compatibility is retained. Hence, it would be better to have the extended interface classes to implement the seekable functions, instead of changing the existing classes.