Added a clause to from_binary/3 to handle bucket type information

This change is needed for MDC replication to be able to handle typed-bucket replication. The "sink" side runs this function after un-marshaling a replicated object, and type information is necessary.

This will depend on Joe Blomstedt's addition of conditional post commit hooks, in this branch:

https://github.com/basho/riak_kv/tree/jdb-conditional-postcommit

The Riak Test for typed bucket replication is here:

https://github.com/basho/riak_test/tree/jra_bucket_types

Additionally, there is a design discussion here:

https://gist.github.com/bowrocker/7f0d9d6879493f1ac0e9