Test replication with CouchDB when more than one leaf revision changed

Here are the tests for couchbase/couchbase-lite-java-core#78, which is a fix for couchbase/couchbase-lite-java-core#77.

One test reproduces the original issue. The other validates the new parameter in the ChangeTracker constructor added en route to fixing the issue.

Also had to update existing change tracker tests to use the new constructor.

As I said in the other PR, there are a bunch of ways to go about making the required changes to make the main test case pass, so feel free to change/redo however you need.

Also, sorry for requiring a remote DB for the test again. Now that we know the issue maybe we can work backwards to a mocked test.