Merge pull request #1382 from bangerth/further-FEValues-cleanups-19

Documentation update of MappingCartesian.

diff --cc source/fe/mapping_cartesian.cc
index 53903d10b747627204ab4ba694e84d79da0a7c2d,c4c4ec1cc6fd5e5c018c67e83739dfefaa005b08..6b192da404673745604deec858795d68ba7c1f04
--- 1/source/fe/mapping_cartesian.cc
--- 2/source/fe/mapping_cartesian.cc
+++ b/source/fe/mapping_cartesian.cc
@@@ -829,10 -838,9 +838,10 @@@ MappingCartesian<dim,spacedim>::transfo
              for (unsigned int k=0; k<spacedim; ++k)
                {
  
-                 output[q][i][j][k] = input[q][i][j][k] / data.length[j] / data.length[k];
+                 output[q][i][j][k] = input[q][i][j][k] / data.cell_extents[j] / data.cell_extents[k];
  
                }
 +      return;
      }
      default:
        Assert(false, ExcNotImplemented());