Irregular meshes now seem to be converging well (that they weren't before was possibly related to the final timestep bug), so have put them into darcy_impes_mms_p1_2phase_quadraticrelperm.  Testing of capillarity now takes place in darcy_impes_mms_p1_2phase_coreyrelperm.  Expected convergence rates have been tightened from 0.6 to 0.8.