BUG: improved landmarks pattern for straightening. Fixed #475
BUG: improved landmarks pattern for straightening. Fixed #475

Former-commit-id: ed818d9db64dc7725399ea412a4a115965248794
Former-commit-id: 5e5e45caeb3552219a48ca22e36f8d9f47638b6f
3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox