The tags are often initially assigned from pointers and then copied
around, even from one tag type to the other.
As BSPTree::MoveSubTreeToArray() uses them to get the original pointer,
we need the pointers anyway, so just CRC-ing the pointers doesn't seem
like a good option. As the tags are assigned from other tag-types
sometimes, I probably would have needed to add Pointers for the same
values in addition to the ULONG tags, that are also copied around along
the tags, to keep the tags ULONG - that seemed like a worse alternative.
However, when writing (via BSPTree::Write_t()) the bn_ulPlaneTag tag
needs to be ULONG, so there I actually use CRC for 64bit pointers (via
IntPtrToID()) - when restoring (in Read_t()), the pointers aren't valid
anymore anyway, so that all should somehow be fine.
I assume that Write_t() is only used by the Editor, anyway, so I fear I
won't be able to test that part of the code on Linux anytime soon.