ENH: Allow use of nibabel
ENH: Better options
Merge pull request #526 from Eric89GXL/nibabel-xfm

ENH: Allow use of nibabel
ENH: Better vertex_to_mni test
ENH: Use BallTree nearest neighbor search
cleanup
Merge pull request #528 from mluessi/compute_nearest_balltree

ENH: Use BallTree nearest neighbor search
FIX: Fixing transform for vertex_to_mni
Working version which also accepts two channels as input. diffs should
show ALL differences that have resulted while adding new option.