Relax assertion after adding a doc, since it might not necessarily be the same exact object (though, will represent the same doc and have same doc id)
Reproduce issue #72 - Push replicator is trying to send all documents simultaneously

https://github.com/couchbase/couchbase-lite-java-core/issues/72
Test for new Batcher implementation - issue #72

https://github.com/couchbase/couchbase-lite-java-core/issues/72
Rename Batcher2 -> Batcher
Test enhancements for reproducing issue #72 - add assertions

https://github.com/couchbase/couchbase-lite-java-core/issues/72
Got a concurrent modification exception, this should avoid it.
update submodule