OPT: add main to avoid system calls
OPT: add main to avoid system calls

Former-commit-id: 8566d3d19fee668b5307f7972335371f62f6d9f5
Former-commit-id: 89cc43d447c4b523f7c73bae89d4c6517829d750
3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox