A statem eqc test  for ro:merge that uses DVVSet for a model

Add copious comments and a command for stale puts
Move put merge code inside riak_object

Since the put_merge code was copied into two tests, both of which
only manipulate riak_object, it seemed a refactor made sense.

Looking at the put merge code, it only manipulates internal state
of riak_object, so I think it is the correct place for the code.

It also smooths the way for a general refactor of riak_object
into a CRDT and riak_kv into riak_crdt (mwah ha ha ha ha!)
Merge pull request #835 from basho/rdb/robj-merge-eqc-rebased

Rebased push of riak_kv#807 (put_merge refactor + EQC)