Blender Git Loki

Fix for bug #6629 - modifiers and vertex-parenting

I have changed the vertex parenting code to use the derivedFinal mesh rather
than derivedDeform; this gives the result after all modifiers have been
applied, rather than the result up to the first non-deforming modifier as it
did before. Since the derivedFinal mesh can have more than one vertex
corresponding to a single vertex in the base mesh, the average of all such
vertices is used.