Made UndefinedStatDeserializer global

Changed so that the UndefinedStatDeserializer will always
be used rather than just on specific stats.

fixes #208
Merge branch 'gh153-expose-head' of github.com:basho/riak-java-client into gh153-expose-head
Small change to javadoc
Merge pull request #194 from basho/gh153-expose-head

Expose FetchMeta.headOnly() in FetchObject
Fixed javadoc
Merge pull request #195 from basho/gh157-expose-deleted

Fix Tombstone handling, expose to client.
Merge pull request #209 from basho/gh208-deprecated-stats

Made UndefinedStatDeserializer global