Fix: Selector couldn't be given as an API instance with indexes

- It is useful to be able to filter row indexes by a condition and then
  operate on the resulting array of indexes, but before the selector
  would only itterate over real arrays. So if you passed is an API
  instance with the result set being the indexes to delete, it wouldn't
  work!

- Fix is to loop over anything which has a `length` property

- Thread 20572
Fix: Accessiblity - Add `role=row` attribute to table rows

- Feedback from James Craig on improving the accessiblity of DataTables.
  Since the `role=grid` option is added to the DataTables table, we
  should also add `role=row` to the rows in the table so the browsers
  can see them correctly. As James notes, it is debatable if this is
  needed or not but it is required in current Chrome and Webkit.

- Webkit do now allow roles to be optional in the nighties - see:
  https://bugs.webkit.org/show_bug.cgi?id=131819 . Once Apple deploy
  this in a Safari update, and Chrome also deploy support, I think this
  should be removed from DataTables core, since it will no longer be
  needed in the latest browsers, and manipulating the DOM can hit
  performance a bit.