Clear the column as well, for great justice

With this change, we're back at r4848 (modulo cosmetic changes)

Oliver and I agreed that this change does not break anything.
Carsten and I agreed that it's not a bad idea.

[[Imported from SVN: r4857]]

dune/solvers/iterationsteps/blockgsstep.cc

@@ -64,8 +64,16 @@ void BlockGSStep<OperatorType, DiscFuncType, BitVectorType>::iterate()
                 if ((*this->ignoreNodes_)[i][j]) {
                     r[j] = 0;
 
-                    for (int k = 0; k < BlockSize; ++k)
-                        matRes[j][k] = (k==j);
+                    for (int k = 0; k < BlockSize; ++k) {
+			if (k == j)
+			    continue;
+
+			matRes[j][k] = 0;
+			// Since r[j] is zero anyway, this changes
+			// nothing but simplifies solving
+			matRes[k][j] = 0;
+		    }
+		    matRes[j][j] = 1;
                 }
             }
             matRes.solve(v, r);