fixed FixedConstraint & PartialFixedConstraint for size-varying mechanical objects

git-svn-id: svn://scm.gforge.inria.fr/svnroot/sofa/trunk@9448 b7f1a160-662a-0410-a6d8-bea165342f16
multimapping : done
work in progress

git-svn-id: svn://scm.gforge.inria.fr/svnroot/sofa/trunk@9449 b7f1a160-662a-0410-a6d8-bea165342f16