Until now, the static part of the grid check only check on codim 0 structures, e.g., on the index set. This patch also performs these checks on higher codimensions.
For the IndexSet::subIndex method, it will only check whether the method compiles. If codim > 0, it will silently ignore a Dune::NotImplemented exception, so that grids are not forced to implement the method; it simply has to compile.
Note: This check is able to detect the error fix in !86 (merged).