Blender Git Loki

Move curve's boundbox and texspace calculation out of modifier stack

There were several issues with how bounding box and texture space
are calculated:

- This was done at the same time as applying modifiers, meaning if
several objects are sharing the same curve datablock, bounding
box and texture space will be calculated multiple times.

Further, allocating bounding box wasn't safe for threading.

- Bounding box and texture space were evaluated after pre-tessellation
modifiers are applied. This means Curve-level data is actually
depends on object data, and it's really bad because different
objects could have different modifiers and this leads to
conflicts (curve's data depends on object evaluation order)
and doesn't behave in a predictable way.

This commit moves bounding box and texture space evaluation from
modifier stack to own utility functions, just like it's was done
for meshes.

This makes curve objects update thread-safe, but gives some
limitations as well. Namely, with such approach it's not so
clear how to preserve the same behavior of texture space:
before this change texture space and bounding box would match
bevelled curve as accurate as possible.

Old behavior was nice for quick texturing -- in most cases you
don;t need to modify texture space at all. But texture space
was depending on render/preview settings which could easily lead
to situations, when final result would be far different from
preview one.

Now we're using CV points coordinates and their radius to approximate
the bounding box. This doesn't give the same exact texture space,
but it helps a lot keeping texture space in a nice predictable way.

We could make approximation smarter in the future or add operator
like "match texture space to object's bounding box".