users will need to use add_forced_doxygen_target instead of
add_doxygen_target in their appropiate CMakeLists.txt

Discovery of eigen3 was brokn for me. Although pkg-config would find the
local eigen3 installation pkg_check_modules would not find it. Since the
FindEigen3.cmake does support hints fora dditional search dirs I hardcoded
the additional location which is currently used by out setup.

Drop support for override and final keyword discovery since all supported
compiler understand those by now. Further use of DS_OVERRIDE or DS_FINAL
will trigger a compile error.

Can now be used in the pure cmake as well as in the autotools/cmake
situation. In the end GRIDDIM and GRIDTYPE are define as cached variables.

This reverts commit 2e8a29f9f02fae28920147e17fc0406a57ca8524
and should work now since we're shipping the FindEigen3
script that's apparently missing from some current
cmake distributions

This reverts commit 043fbca5cadb4e4ef7909df0049aef350bb61d89.

refs #5

This reverts commit b5e571fc9ad2240d510514566c0946b2cce23426.

At the moment it is not trivial to configure a debug build with e.g. -O2.
Upon calling make cmake is called and the CMAKE_CXX_FLAGS_DEBUG are
appended to any given CMAKE_CXX_FLAGS, thus overriding any -O? given there.
Since the desired debug flag might vary from compiler to compiler
(-O0, -Og) anyway I propose to remove the -O? entirely from the debug
flags. Please revert or voice opinions!

* ensure dune-commons cmake stuff is used only with --use-cmake