Trade brevity for clarity

[[Imported from SVN: r4607]]

dune/fufem/symmetrictensor.hh

@@ -54,7 +54,7 @@ public:
     {
         double r = 0.0;
         for (int i = 0; i < dim*(dim+1)/2; ++i)
-            r += (1+(i>=dim))*(*this)[i]*B[i]; // this weird looking coefficient is used to produce the 2 as coefficient before the off-diagonal entries which occur twice in the full (symmetric) matrix 
+            r += (i>=dim ? 2 : 1)*(*this)[i]*B[i];
         return r;
     }