Port Latest AAE Changes

More changes were made during Riak 1.3 testing which must be ported to Yokozuna.  These are blockers on 0.3.0 release since yokozuna_essential is having AAE related failures.  Not all of these changes necessarily apply to Yokozuna AAE.

* <del>basho/riak_kv#460 (AAE Exchange Bug for N=1)</del>

* <del>basho/riak_kv#472 (Various AAE Changes Prompted by QA)</del>

* <del>basho/riak_kv#473 (Don't Repair Over and Over)</del>

* <del>basho/riak_kv#474 (Fix AAE Rehash When Data is Missing)</del>