minc_displacement ignores dimension order

[mcvaneede]

minc_displacement creates output files that always have the same dimension order:

vector_dimension
    zspace             
    yspace             
    xspace             

regardless of the dimension order of the input.mnc file. (This can cause issues in pipelines where the stats files are created with a different dimension order than the other files. Some tools (RMINC) don't like this...)