[Dune] unreached headers in DUNE

[Christian Engwer]

> >>IMHO Removing unreached headers might be dangerous.
> >I agree. I was not suggesting to remove them without any further
> >consideration. I only wanted to mention that there are files which are
> >not being tested in the core modules themselves. If you are fine with
> >that, I am totally happy for you. IMHO of course.
> >
> 
> You are right.  Any API file provided by a module should be tested
> in that module, even if not used anywhere else.  I am afraid though
> that I cannot say here much more than 'patches are welcome'.

The major problem is that we are talking about C++ & templates. This
means that the usual coverage analysis doesn't work, as each code
snippet can produce substatially different results depending on the
template parameters. This means we can do hardly more than syntax
checks by including the code some where.

While it is good to see which files are included already, it is not as
bad as expected if a file is not included from a cc file. We have the
"make headercheck" target to run test against all headers. This means,
that a dummy cc file is generated during the test which includes the
header.

Just as a bit of additional information...

Christian