[numerics] fix bug in SparseMatrix test and (partly) clean memory leaks
[numerics] fix bug in SparseMatrix test and (partly) clean memory leaks

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