Bookshelf download time should not raise with the number of documents

[benel]

With current implementation: 11s for 865 documents (measured directly on the backend).

The delays exists only when reduce is enabled.

[benel]

The problem is hard to reproduce...

The following command now runs (locally) in 1s for 337 CouchDB documents:

curl http://localhost:5984/hyperglosae/_design/app/_view/all_documents\?reduce\=true\&group\=true >/dev/null

More tests would be necessary.

[benel]

Although the download time doesn't raise as fast as we feared, the index should be paginated so that its download time is not proportional of the number of documents.

[benel]

The delay was probably caused by the "reduce" part of the view.

Commit 84e4e3e probably solved this (at least for now).