Added capillary pressure and residual sats to darcy_impes_mms_p1_2phase_quadraticrelperm tests, but there is a problem with capillary pressure: convergence is spoiled in higher dimensions.  There are other strange effects, such as sum(div(u) - q) no longer reports as zero, and paraview shows NaNs for capillary and phase-2 pressure.  Need to investigate.
Fixed bug in Python code; tests with capillarity now working.