Needs refactoring!

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.