Added the necessary support to load a real NIMROD file.

Title says it all - I was helping somebody out to load a NIMROD file, and I needed to make these changes to load it (and couldn't resist with the others).

For a specification of NIMROD, please search for [site:es.lancs.ac.uk "nimrod file format"](https://www.google.co.uk/search?q=site:es.lancs.ac.uk+%22nimrod+file+format%22)