Avoid additional auto-boxing in NonBlockingSetInt.

Overloads addAll(), removeAll(), containsAll(), retainAll(), hashCode(),
and toString() to avoid auto-boxing. Fixes some miscellaneous JavaDoc
issues and other small code changes.
Merge pull request #3 from pkwarren/avoid_more_autoboxing

Avoid additional auto-boxing in NonBlockingSetInt.
Add NonBlockingHashSetLong and fix bug.

Add NonBlockingHashSetLong (with additional improvements to avoid
auto-boxing). Fix a bug in retainAll() in NonBlockingSetInt (wasn't
properly returning the 'modified' value. Added a test to verify the
behavior of retainAll().
Merge pull request #4 from pkwarren/non_blocking_hash_set_long

Add NonBlockingHashSetLong and fix bug.