ignore unknown command line arguments

I did as Atgeirr requested and tried to compile the release branch of all modules using openSUSE 12.2 and using dunecontrol. I had some issues with the configure script (patch attached) and much serious issues because my CMake refuses variable names which contain a '-'. On the latter issue I gave up after half a day. Does anyone have an idea how to fix this? the issue probably does not occur if you only compile opm-core, because I suspect that cmake ignores everything before the last '-', and the macros are only invoked once in this case...

NB: Although I picked dune-cornerpoint as the target repo, this patch should be applied to all CMake enabled OPM modules.