Merge branch 'master' into soc-2020-io-performance

Add more regression tests for new obj exporter.

This adds regression tests for exporting most of the blend files
in the io_tests/blend_geometry and io_tests/blend_scene tests.
A fix was necessary in the BlendfileLoadingBaseTest class to prevent
leakage of some global data generated when a loaded file has metaballs.
Also, had to fix the exporter to deal with empty curves.

Merge branch 'master' into soc-2020-io-performance

Fix T91889 Exact boolean sometimes drops triangles.

The problem is that the fast triangulator (based on polyfill)
sometimes makes degenerate triangles. Commit 8115f0c5bd91f had
a check for degenerate triangles but it wasn't thorough enough.
This commit uses a more thorough (and pessimistic) test for
degenerate triangles, using the exact triangulator in those cases.

Fix T91810 Bevel not working well with certain unbeveled edge positions.

A previous commit, c56526d8b68ab, which sometimes didn't drop offsets
into 'in plane' faces, as a fix to T71329, was overly aggressive.
If all the intermediate edges are in the same plane then it is fine
to just put the meeting point on the plane of the start and end edges.

Merge branch 'master' into soc-2020-io-performance

Merge branch 'master' into soc-2020-io-performance

Fix mistake with last commit - it didn't compile.

Change where new obj exporter writes temp files.

The code was writing relative to the test_release_dir flag,
but this didn't make a lot of sense.
Better to use Blender's tempdir mechanism, though since Blender
isn't fully initialized when using it for gtests, we have
to call the function to initialize the tempdir.

Merge branch 'master' into soc-2020-io-performance