Overall, a really useful and functional addition - thank you!
I agree with John D'Errico that some more detailed comments/help would have been useful. Also, there's some typos in the comments header. That's really the only reason this is not a 5.
However, since the script is not meant to find an orthogonal basis, I don't think see why that should be a negative point. As I understand it anyway, orthogonal bases tend to be dense anyway - if you really need an orthogonal basis of the null space you can use the lower part of Q^{T} from a QR factorization.
I would like to see it upgraded using Tim Davis' suggestion (although dmperm now uses the code from CSparse.)
