headercheck does not compile anymore.

There have been some recent changes in dune/grid/test and dune/grid/identitygrid that make the headercheck fail.

@linus.seelinger : Please fix the test/yasp things @oliver.sander : Please fix the identitygrid things

or use cmake macro

exclude_from_headercheck( header-name )

to remove failing headers from the list of headers to be tested.