Object update used to free object-data level bounding box to trigger
it's re-calculation in the future. Such a freeing performed from
object update isn't thread-safe because mesh could be shared between
multiple objects.
Rather than freeing bounding box, tag it's as invalid, this is safe
from threading point of view and also prevents unnecessary memory
re-allocation.
Object-level bounding box is still reallocating, but think we could
change this easily in the future as well.
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svn merge -r58154:58156 -r59258:59259 ^/branches/soc-2013-depsgraph_mt
f030758515