(#2342) - WIP - failing test for changes

@calvinmetcalf This may just be me being dumb, but I'm trying to write a reproducible unit test for #2342, and for some reason when I call db.changes I don't get any callback on either `change` or `complete`.  I tried every combination of event emitters as well as the old style (which you see here) and nothing works &ndash; radio silence.  Looking at the code, it seems to keep tunneling into `doChanges()` forever, decrementing the `since` to negative infinity.

I think it might be a separate bug.  Ideas?