Blender Git Loki

Fixed several filtering bugs.

Several bugs with the acceleration filters cauased crashes and
incorrect results. Redid the error analysis and found some mistakes.
There was also a bug in the code for checking non-trivial intersections.
Now you can boolean a standard cube and cylinder and scale the cylinder
without crashing.
Also rewrote the tri-tri intersection code to make it more understandable
and also prepare the way for more floating filters.