Fixing what I think is a bug with property updates on fetch requests

I have been writing a AFIncremental store to use against CouchDB.

I was having issues with a TableView getting property updates on objects.

The context being used for fetch requests were being nil'ed out and never firing change updates on properties.

I have tested this on a large import from Cloudant with over 1000 records and it never blocks the UI thread and properly send out change notifications for all properties.