Squashed 'cmake/Modules/' changes from fe76bc7..0f6a2d4

0f6a2d4 fix of linking problem with CGAL and BOOST libraries
9de5244 refining mpi compile flags handling
3eed328 PackageSystem correction
5592c02 ensuring that every element are tested
2ed7d7f Modified cmake to declare the element info in the packages
e9e79fd Changing the way the pacakge system is coded to factorize code

git-subtree-dir: cmake/Modules
git-subtree-split: 0f6a2d4e60396af911baccd4d091139a906ea462