Pull replication by doc-IDs, from a CouchDB version < 1.1.0, no longer works when sent from a CouchDB 1.1.0+ server

After Benoît added the built-in _changes filter _doc_ids to trunk (and now in 1.1.x as well), I updated the replicator to use it for the replication by doc-IDs. The advantages of this are:

1) Elimination of very specific, and harder to maintain, code from several replicator modules;
2) Allow for continuous by doc-IDs replication (this was not possible before because a replication by doc-IDs didn't use the _changes stream at all)

The change was done in the following commit:

https://github.com/apache/couchdb/commit/5afece2131f4ef4000d768b671bddbbf714303d9

It happens that with the branch 1.1.x (and trunk as well), it's no longer possible to pull replicate by doc-IDs from previous CouchDB versions (since they don't have that new built-in filter).

The following patch fixes the issue by changing only 1 module of the replicator. If no objections, I'll commit it later.