1 - Clean some parts

2 - Add a task based fmm threaded algorithm.
    It uses the OpenMP task (but needs some test)
    Now there are 3 multi thread fmm algorithms
        Naive approach (iter + mutex)
        Task based approach
        Inspector-executor model (closest to fmb original approach)

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/scalfmm/scalfmm/trunk@27 2616d619-271b-44dc-8df4-d4a8f33a7222