Add reset bucket properties (Riak 1.3) Issue #94

* Added ResetBucketProperties(string bucket).
* Added live unit test.
* Added details to the release notes.

Despite running Riak 1.3 RC, I wasn't able to use /buckets instead of
/riak when setting or getting bucket properties. Not sure why. Instead
of using /buckets for everything we're still using /riak for other ops
but have to use /buckets/<bucket>/props for this new operation.