register the message even if it's already there with the same payload so that the...

register the message even if it's already there with the same payload so that the old payload gets free'd when its refcount becomes zero; make a gras_msg_recv_no_malloc function to make clear that if you don't NULL its argument, you'll get into trouble (interface simplification again)

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/simgrid/simgrid/trunk@135 48e7efb5-ca39-0410-a469-dd3cf9ba447f