Issue #253 make it easier to debug async task count issues.

https://github.com/couchbase/couchbase-lite-java-core/issues/253
Closes #253 - workaround to check the online flag within the async task, and prevent excessive change trackers.

https://github.com/couchbase/couchbase-lite-java-core/issues/253
Issue #255 - fix attempt

https://github.com/couchbase/couchbase-lite-java-core/issues/255