mrtransform: remove debug write-out of transforms
NIfTI: make transformation adjustment available as standalone function
mrtransform: minor cosmetic change
new command 'mtxedit' to convert transform matrices

Currently only works if both input and reference images used in the
flirt call have 'standard' strides - i.e. standard orientation in
FSLView. Still working on getting things to work for the more general
case.