Blender Git Loki

Fix some issues with image previews.

* When overlaying icon, we have to also ensure background pict is always the same size
(else you get usgly icon size changes). Still not perfect though, suspect some more issues
in filrdraw code, probably should systematiacally run the 'ensure size' code during thumbnail
generation?
* Sharing of img ImBuf between thumbnail job and main thread could still happen,
leading to random crashes.

Fix py script generating obj/group previews after recent merge.

Merge branch 'master' into asset-experiments

Conflicts:
source/blender/blenkernel/BKE_camera.h
source/blender/blenkernel/intern/camera.c
source/blender/blenlib/BLI_fileops.h
source/blender/blenlib/intern/storage.c
source/blender/editors/space_file/filelist.c
source/blender/makesrna/intern/rna_object_api.c
tests/gtests/blenlib/BLI_path_util_test.cc

Properly register `mathutils.bvhtree` as a submodule.

Added mathutils.bvhtree submodule to the excluded modules list in
the sphinx doc build files.

Nicer doc strings for BVHTree subclasses.

Distinguish `use_poly_index` flag based on FACES/POLYS type instead of
an explicit argument.

This avoids meaningless cases when setting `use_poly_index` for vertex
or edge BVHs and is nicer for bmesh which does not yet support both
index types (only polys). Eventually BMeshBVHTree could support
tessfaces as well, at which point it could get a similar type enum.

Simplified dm_tessface_to_poly_index, no need to keep two version of
this around.

Splitting the BVHTree python type into two distinct subclasses for
DerivedMesh and BMesh support.

This avoids messy code due to mixed data in the same py type. And makes
it clear at any point what kind of data the BVHTree instance represents.

Both types are based on the common BVHTree type, which currently does
not have any functionality of its own. Eventually it could implement
common BVH functions (find-nearest and ray casting) as well as return
read-only info about the size and type of BVH data.

Note: While the BVH functions already use callbacks for providing a
common interface in C, using this for python types would be redundant.
It also still requires specialized data for some details of testing
elements.

find_nearest implementation for bmesh BVHTree type.

This uses only mesh vertices, since this function is supplied by the
bmesh bvhutils. Nearest face lookup could be added later.

Some fixes for uninitialized variables with bmesh bvh trees.

Support for BVHTree construction and ray casting from a BMesh.

Minor doc string fixes.

Use separate result tuple constructors for ray_cast and find_nearest.

These are technically the same, but the semantics are slightly different
(distance vs squared distance).

Nearest element search method for BVHTree submodule.

Optional argument `use_poly_index` of the ray_cast method.

This allows turning off the default poly_index return value and using
plain tessface indices instead if needed.

The tessface -> poly lookup now also includes a range sanity check.

Added object vertex and edge constructors for the BVHTree type.

Joined the two bvh tree classes in a single type for simplicity.

New mathutils submodule for BVH tree support in python.

Merge branch 'master' into gooseberry