Blender Git Loki

Ugly hack for caching code to deal with quirky modifier stack behavior.

CustomData layers are pruned by the CDDM_copy function when they have
CD_FLAG_NOCOPY set. This is based on later modifiers in the stack, which
can specify that they require certain data layers - but the caching
modifier itself should store only what is needed by later modifiers.
It means we cannot easily keep a full copy of the DM in the cache
modifier to writing into caches later.

For now the hackish solution is to temporarily disable NOCOPY flags when
copying the DM. This is really not nice and needs a better solution.