Add generation and use of warning-suppressing headers.
Avoid warning by not storing MPIHelper instance reference.
The reference phase is always the oil phase. Removed explicit warning.
Remove unused variable.
Use non-deprecated leafGridView() method.
Fix bugs relating to misused face_cells variable.
Merge branch 'master' into suppress-warnings

Conflicts:
	cmake/Modules/UseWarnings.cmake
Use #if guards to handle different dune versions.
Add missing #include.

While version.hh is included transitively via other dune includes,
this may change. So for future-proofing we include it here.
Merge pull request #122 from atgeirr/suppress-warnings

Suppress external and other warnings