Modified system test Relax_disp.test_cpmg_synthetic_ns3d_to_cr72 to catch bug.
bug #22017: (https://gna.org/bugs/index.php?22017) LinAlgError, for all numerical CPMG models.
Systemtest was renamed from test_cpmg_synthetic_cr72 to test_cpmg_synthetic_ns3d_to_cr72, to
reflect which model create the data and which model fits the data.
