I tried to carefully preserve all patches since the last upgrade.
Improves T47195, cloth collision detection bug.
Differential Revision: https://developer.blender.org/D1739
add PhysicsConstraints.exportBulletFile(char* fileName) python command
I'll be checking the bf-committers mailing list, in case this commit broke stuff
scons needs to be updated, I'll do that in a second.