Blender Git Loki

Fix crashing accessing normals out-of-bounds.

Normals in Alembic can either be per-face or per-vertex, so read the
normals according to their scope. Face normals are not read at the
moment since I couldn't figure out how to read the data and there are
some other annoying crashes that need to be fixed beforehand.

Handle job cancelation.

Cancelling an export will remove the exported abc file from disk.

Cancelling an import will simply stop reading/processing the data, still
needs to remove created objects from the scene.

Fix constraint not working with relative paths.

Some improvement to custom data reading:

- split custom data reading from AbcMeshReader
- Only add UVs to meshes if the ISchema has some, use proper UV name for
the {I|O}Schema.
- Fix crash reading mcols from other software.

Fix crash accessing invalid property headers.

Merge branch 'master' into alembic_basic_io

Split customdata writing in separate files, de-duplicate some code.

Remove outdated/bogus customdata writing code.

Add support to read and write vertex colors.

Rename AbcHairReader -> AbcCurveReader.

Add static qualifier.

Don't call BKE_nurb_knot_calc_u on curve paths.

Use a DerivedMesh to stream curve data as well.

Simplifies the code a bit.

Slight cleanup.

Pass compound prop to write_extra_uvs instead of the schema.

Fix crash accessing invalid IPolyMeshSchema.

Add Alembic to install_deps.sh.

Merge branch 'master' into alembic_basic_io

Conflicts:
source/blender/blenloader/intern/writefile.c

Add a filter for Alembic files in the file selector.

Quiet warning.