Bugfix: order of function arguments.

Order of arguments for computePhaseFlowRatesPerWell() was wrong.
This fix was done previously for SimulatorCompressibleTwophase,
but the incompressible sim was ignored.

Also added an ASSERT that may help catch some misuse.

opm/simulators/SimulatorIncompTwophase.cpp

@@ -485,8 +485,8 @@ namespace Opm
                 // Optionally, check if well controls are satisfied.
                 if (check_well_controls_) {
                     Opm::computePhaseFlowRatesPerWell(*wells_,
-                                                      fractional_flows,
                                                       well_state.perfRates(),
+                                                      fractional_flows,
                                                       well_resflows_phase);
                     std::cout << "Checking well conditions." << std::endl;
                     // For testing we set surface := reservoir