OPT: improved pipeline for straightening
OPT: improved pipeline for straightening

Former-commit-id: bc5d98062899abead9e575baf68e2c1b14c1d0d0 [formerly cef51f1557bb15166cbeb438d1a83c496fdfa7e3]
Former-commit-id: da2e2823a71c5cb99484f72c8893b738789013ef
Former-commit-id: 0362eb79c3a0848e0918441b8cdeabe0e26821cb
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox