[dune-fem] [Dune] Gmsh reader and boundary Ids

[Andreas Dedner]

Hi everyone.

There was a quite a severe bug in the dirichletconstraints class from 
the dune-fem-howto
for distributed grids. I updated the release-1.4 branch of the howto on 
the dune wiki. There are
basically two things that needed to be fixed with the correct treatment 
of dirichlet dofs which are
on process boundaries (have slave copies on some other process).

If you need to see the changes you can use
git diff --ignore-space-at-eol -b -w 
dbc6b4a361eeb81ba9ceb162217d0793df598057 
04.poisson-2/source/dirichletconstraints.hh

Hope that fixes the issue but let me know if the commit broke something 
or if you find some new problem...
Best
Andreas

Teaser:
we will be making some small changes to the model interface to make it 
more general.
These changes are necessary to be able to easily implement
      - more general boundary conditions (we want to add Robin and 
Neuman to the poisson example)
      - a stokes solver (we will add an example for (quasi) stokes and 
possibly navier stokes)
If someone wants to help let me know....