Fix rectilinear grids.

We had i and k backwards because it is inconsistent in xdmf
(all versions). Before it would crash once you tried to use
(filter on or display) the attributes. Now it doesn't and the
rectgrid datasets are actually correct in paraview whereas
with xdmf2 they weren't.

Change-Id: I484a0b5bbe372f95a7420c28b4c059b1d92a1b25