[io] mechanics_run: fix #263 with option 3, without warning
[io] mechanics_run: fix #263 with option 3, without warning

siconos/siconos,siconos/siconos,radarsat1/siconos,fperignon/siconos,fperignon/siconos,fperignon/siconos,radarsat1/siconos,radarsat1/siconos,fperignon/siconos,fperignon/siconos,radarsat1/siconos,siconos/siconos,radarsat1/siconos,siconos/siconos