This fixes two issues:
* Normals were not being recalculated correctly when not using optimized
drawing for CDDerivedMesh (Multires actually handles that correctly).
* Loop normals (autosmooth option) were also not being calculated. Doing
this calculation is not desirable, since it can't be done correctly
without a severe performance hit. This is easy to test by doing a
dependency flush on the mesh after each scuplt stroke step. Instead they
are now disabled during sculpting.
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