OPT: straighten_spinalcord: changed default threshold_distance=10 (issue #1182)
OPT: straighten_spinalcord: changed default threshold_distance=10 (issue #1182)

Former-commit-id: a1519e60945895016e98f0928a1f82531bb670c1
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox