[Dune] dune-grid r4244.

[Christian Engwer]

Hi Robert,

> the purpose of this patch is to revise the code of the DGF parser in 
> order to compile this code into the grid lib to speed up compilation 
> time of user code. Also dimension != dimensionworld is currently not 
> running which is also changed by Martin and needed for one of our
> projects.

I think it is good to compile the dgfparser int the lib. But this was
not part of the patch in question.

> Furthermore, things like the grid type should not be in one file that 
> cannot by expanded easily.

About this point I'd like to discuss. The gridtype.hh is a hack to
allow stear your program using preprocessor defines. Tere are reasons
why people like to have something like this, therefor it was provided
as a utility. It should not be something to rely on. Now the latest
changes made this part of the interface. Every grid has to provide the
code to deal with these preprocessor switches.

I don't like the idea of preprocessor macros being part of the
interface. We tried to avoid them as much as possible.

Cheers
  Christian