DLM to share data from DerivedMesh (reduces some copying/memory allocation) - added displistmesh_copyShared function to copy a DLM but not duplicate any internal data - changed crease drawing to use DerivedMesh functions... this means varying edge width style of creases had to go, I replaced by using varying color to show crease weight instead. Don't think this is a big loss since the subsurf result gives you a much better indication of the crease weight anyway. - bug fix in mirror modifier, didn't copy edge creases from editmesh correctly