CMake rollup in anticipation of the 2013.09 release

This changeset synchronize the build system with the canonical version in opm-core.

From this point on I suggest that changes to the `cmake/` directory is not admitted unless there is a corresponding commit in opm-core first. Preferrably these should also be isolated from other changes, as that will be easier to cherry-pick into the other modules. 

Maintainers: Please hold until there is a rollup package available in every module, as further issues may surface.