Matrix: Replace the row-start pointer array with computed offsets

The row-start pointer array provided performance benefits on old
computers but now that computation is often cache-miss limited the
benefit of avoiding a integer multiply is more than offset by the
addition memory access into a separately allocated array.

With the new addressing scheme LUsolve is 15% faster.

src/OpenFOAM/matrices/scalarMatrices/scalarMatricesTemplates.C

@@ -56,8 +56,6 @@ void Foam::solve
 
         if (i != iMax)
         {
-            //Info<< "Pivoted on " << i << " " << iMax << endl;
-
             for (label k=i; k<m; k++)
             {
                 Swap(tmpMatrix[i][k], tmpMatrix[iMax][k]);