[Dune] better DEPRECATE

[Andreas Dedner]

Hi.
We should really try to document what to replace deprecated method with:
That is really important for the users I think.
GeometryType::basicType() is for example used in the virtualrefinement
and I do not really know what to replace it with.

Andreas

PS: Compiler output
/grid/common/virtualrefinement.cc:489:105: warning: 
‘Dune::GeometryType::BasicType Dune::GeometryType::basicType() const’ is 
deprecated (declared at 
/home/maths/masjal/DUNE/dune-common/dune/common/geometrytype.hh:246)
There are two more places in dune-grid:
./common/test/test-genericquadrature.cc:28: switch (t.basicType())
./common/test/test-quadrature.cc:25: switch (t.basicType())