WIP bucket types
Make riak_object speak bucket types
Sanitize the default bucket type out at the vnode layer

The vnode is unlikely to see this unless the user is using
riak:local_client, but better to be safe.
More API changes to support bucket types
Teach mapreduce about bucket types
Fix bucket folding for bucket-types and eleveldb
Fix bug where queue_existing_pipe did not decode bucket correctly

When a key-filter was being used, pipe would do a get_bucket with the
{Bucket, Filter} tuple, which would return the default bucket
properties, thus potentially using the wrong n_val for the coverage
query.
Fix bucket folding when bucket type is undefined
Fix guard to avoid passing undefined as Client pid
Merge branch 'bos-bucket-type' into develop