Reduced max memory usage of push replicator

- Added some fixes to avoid keeping redundant data in memory
- Constrained max size of a _bulk_docs request to keep the object tree from getting too large
Fixes #270
Removed “Slow comparison” log message from JSON collator

This wasn’t supposed to be checked in…
Add a unit test while comparing conflict resolution behavior against couchbase-lite-android

https://github.com/couchbase/couchbase-lite-java-core/issues/106
Merge pull request #302 from couchbase/delete_conflict_test

Unit test regarding conflict resolution behavior
Removed support for “_conflicts” property in doc passed to map blocks.

It didn’t work quite right (could miss some conflicts) and taking it out speeds up
view indexing a little bit.
Developers who want to find conflicts should use an allDocs query with the
only-conflicts option instead.
Fixes #159
Fix replicator checkpoint issue by making sure checkpoint doc ID stays constant

Memoize the value returned by .remoteCheckpointDocID so it stays the same even
if a setting changes — namely, the -stop method sets _continuous=NO for some reason.
Fixes #301
Safer handling of unexpected revisions returned from _bulk_get

Don’t process such a revision; it’ll cause an exception later.
For #300
Merge branch 'master' of github.com:couchbase/couchbase-lite-ios