Make TransportSolverTwophaseReorder inherit TransportSolverTwophaseInterface.

This changes the solve() interface, which requires clients to change.

tutorials/tutorial3.cpp

@@ -301,8 +301,7 @@ int main ()
         /// \details  Solve the transport equation.
         /// \snippet tutorial3.cpp transport solve
 	/// \internal [transport solve]
-        transport_solver.solve(&state.faceflux()[0], &porevol[0], &src[0],
-                               dt, state.saturation());
+        transport_solver.solve(&porevol[0], &src[0], dt, state);
         /// \internal [transport solve]
 	/// \endinternal
 

tutorials/tutorial4.cpp

@@ -420,7 +420,7 @@ int main ()
         /// \TODO We must call computeTransportSource() here, since we have wells.
         /// \snippet tutorial4.cpp tranport solver
         /// \internal[tranport solver]
-        transport_solver.solve(&state.faceflux()[0], &porevol[0], &src[0], dt, state.saturation());
+        transport_solver.solve(&porevol[0], &src[0], dt, state);
         /// \internal[tranport solver]
 	/// \endinternal