Add test for CRDT convergence.

This requires a build of Riak using:

* basho/riak_kv#650
* basho/riak_pb#52

riak_test should be built with:

* basho/riak_pb#52 (same as above)
* basho/riak-erlang-client#114

This test follows the same outline as the verify_counter_converge
test, which is to:

1. Write a new datatype into the cluster.
2. Check that the value was correctly stored, via connecting to some
   other node.
3. Partition the cluster.
4. Perform updates on both sides, verifying that the new values do not
   cross the partition.
5. Heal the cluster and show that the data converges according to the
   desired behavior.

There is still one outstanding problem with this test, in that maps
have a "reset" behavior when removing a field; namely, embedded types
would be semantically set to a value that resembles their bottom
value, but is actually higher in the partial-order/lattice. We have
decided this behavior is too surprising, especially in the case of
counters, where concurrent reset-removes would result in a
double-counting problem. See L255 for an example.