Handle unusual transforms by setting dimension order correctly.

[rdvincent]

NIfTI files most commonly have the dimension order x (left-right), y (anterior-posterior), and z (inferior-superior), where z is the slowest-varying dimension (what we call the "slice" dimension in MINC) and x is the fastest. However, NIfTI files can modify this mapping with appropriate changes to the voxel-to-world transform.

The existing code would not properly handle cases where the relationship between voxel and world coordinates didn't conform to the most frequent case. This fix correctly rearranges the transform and the "order" array to reflect the correct mapping for these less common files. The code is very similar to the code in mgh.js that performs the almost identical function.

[natacha-beck]

Just tested and reviewed the code everything seems ok for me. @rdvincent: Do you want a release asap ?

[rdvincent]

@nbeck Yes, it's probably a good idea to do a release soon.