Added CMake support

Build Directory
Put a data directory (data are not on the svn yet)
Remove compilation warning with -wall

Need to forbid use of cmake inside sources directory.

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/scalfmm/scalfmm/trunk@28 2616d619-271b-44dc-8df4-d4a8f33a7222