[Dune] last changes of dgfparser.hh and gridtype.hh

[Christian Engwer]

Hi Andreas,

> I still do not see the advantage of including
> all grid implementations found during configure
> in gridtype.hh - only one typedef GridType
> can be set in any case.

For gridtypehh you are right and I was wrong. There is no use in
including all headers.

I will fix this.

Cheers Christian