cmake+ccache: cmake 2.8.12 can no longer use ccache as the compiler, but it as to be defined in the CMakeLists.txt.
If installed, ccache is now automatically used and only the compilers (ie gcc/g++, clang/clang++) have to be given
in the cmake command while creating the build directory.

git-svn-id: svn://scm.gforge.inria.fr/svnroot/sofa/trunk@11359 b7f1a160-662a-0410-a6d8-bea165342f16