This does not need any code in cmake as the macro is defined by the
compiler itself. See also the table here:
http://nadeausoftware.com/articles/2012/10/c_c_tip_how_detect_compiler_name_and_version_using_compiler_predefined_macros

For compatibility with unported examples, the old typedef is still kept,
but IndexType should be removed from grids eventually.

Adding Gnuplot writer for vector field.

This does not have to be tested and configured manually :)