fix FaceNeighborSubdomain ( update #202 ):
 warning : the ghost cells elt are the elt which share a point,edge or face with an active elt
 so compute this only for elt which share a face
compute stencil on active elt
do nothing if has no elt
fix transpose matrix and operator adjoint (update #202 )
minor up gmshSaveOneElementAsMesh
add  new constructor of PointSet : init a set of point on each face
update #202