Remove the incremental upate of mean molar mass. I.e. the mean molar mass is...

Remove the incremental upate of mean molar mass. I.e. the mean molar mass is re-calculated every time a mole fraction is set. This means more calculations, but before random errors occured. In other words: this is more stable.
reviewed by Bernd

git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@12215 2fb0f335-1f38-0410-981e-8018bf24f1b0

dumux/material/fluidstates/compositionalfluidstate.hh

@@ -272,25 +272,15 @@ public:
         Valgrind::SetDefined(averageMolarMass_[phaseIdx]);
         Valgrind::SetDefined(moleFraction_[phaseIdx][compIdx]);
 
-        if (std::isfinite(averageMolarMass_[phaseIdx])) {
-            Scalar delta = value - moleFraction_[phaseIdx][compIdx];
-
-            moleFraction_[phaseIdx][compIdx] = value;
-
-            sumMoleFractions_[phaseIdx] += delta;
-            averageMolarMass_[phaseIdx] += delta*FluidSystem::molarMass(compIdx);
-        }
-        else {
-            moleFraction_[phaseIdx][compIdx] = value;
-
-            // re-calculate the mean molar mass
-            sumMoleFractions_[phaseIdx] = 0.0;
-            averageMolarMass_[phaseIdx] = 0.0;
-            for (int compJIdx = 0; compJIdx < numComponents; ++compJIdx) {
-                sumMoleFractions_[phaseIdx] += moleFraction_[phaseIdx][compJIdx];
-                averageMolarMass_[phaseIdx] += moleFraction_[phaseIdx][compJIdx]*FluidSystem::molarMass(compJIdx);
-            }
-        }
+		moleFraction_[phaseIdx][compIdx] = value;
+
+		// re-calculate the mean molar mass
+		sumMoleFractions_[phaseIdx] = 0.0;
+		averageMolarMass_[phaseIdx] = 0.0;
+		for (int compJIdx = 0; compJIdx < numComponents; ++compJIdx) {
+			sumMoleFractions_[phaseIdx] += moleFraction_[phaseIdx][compJIdx];
+			averageMolarMass_[phaseIdx] += moleFraction_[phaseIdx][compJIdx]*FluidSystem::molarMass(compJIdx);
+		}
     }
 
     /*!