Removes global locking on interned String

The existing locking scheme was relying on the global string pool and
really introduced far larger scope than necessary.
Merge pull request #197 from basho/gh160-avoid-string-intern

Removes global locking on interned String
Merge branch 'master' of git://github.com/basho/riak-java-client
Merge branch 'master' into temetra-riak-java-client