After indexing a view, its lastSequenceIndexed may be less than db's lastSequence

[snej]

As reported in couchbase/couchbase-lite-ios#1379 , after a CBForest view is indexed, the lastSequenceIndexed stored in the view may still be less than the database's lastSequence. This marks the view as not being up to date, so the next time it's queried it will get indexed again (with the same results, if the db hasn't changed.) This is bad for performance.

[snej]

The MapReduceIndexer is only updating its last-sequence when it gets called to index a document. So if the last document(s) in sequence order are ones that don't get indexed — like design docs or docs whose docType doesn't match — the last-sequence won't end up equal to the database's last-sequence.

I think the best fix is to stop updating last-sequence every time a document is indexed, but just update it to the database's last-sequence at the end of the indexing, before saving the index metadata.

[snej]

Fixed by 9c0af6b