OPT: improved straightening
OPT: improved straightening

Former-commit-id: 580dc42cab10ad907336f114c1ee83051666ad7b [formerly 92a3463da36e12adeb9124714ce14eea8b30d745]
Former-commit-id: d822fcee04e40a6563a581b8caa618ceaa9c123f
Former-commit-id: 62b39f797ca22947293bd81fe757800111cbbd0e
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox