Get Ektorp to more flexibly handle getAllDocIds() responses

I am working with CouchBase Lite for Android and when I use Ektorp to make a getAllDocIds() call the call fails because CouchBase returns _conflicts data by default. Strictly speaking this is a bug in CouchBase since Ektorp didn't supply the argument on the request that explicitly asks for conflict data and by default the argument is false.

Nevertheless I suspect it's good practice for Ektorp to be flexible in what it accepts. I think that was actually the purpose of the existing code but one edge case, putting an array inside of a row field value, tripped it up. 

This pull request makes the code handle the _conflicts case. A quick test is also added to test the functionality.