Indexes are nice; propertyNameForSectionGrouping is important bugfix

Mainly pull for 5b63e4a which fixes a bug I was having where section 0's "objects" list included section 1's rows during calls to -(UIView*)tableView:(UITableView*)tableView viewForHeaderInSection:(NSInteger)section
.  Might as well pick up the index implementation from appunite/TAFetchedResultsController at the same time :)