Initial cpu-only Release

This is a long-overdue update to the BulletSim C++ wrapper in OpenSimulator. I have introduced two main updates:

1. Increase sub-step resolution and filter by context impulse

This introduces two default values that ought to be changeable on the C# (OpenSim) side of things. For now they're set to values that might mimic what ubODE or Havok do. People complain about BulletSim, but they have it backwards. BulletSim does its job so well that we have to back it off a bit to make it act like the other engines. That's what these values are for. We can now dial in what we want, but as of this moment we will need to recompile to do so, hence the default values. Upstream can catch up later while we use this.

DEFAULT_MAX_SUBSTEPS
DEFAULT_CONTACT_IMPULSE_THRESHOLD

Specifically, it ignores small collisions.

2. Hollow and cut prims implementation

This is to fix the issue of not being able to walk through hollow objects. I tested it and can walk through hollow objects now. I can even drop a sphere into a pipe with no problems! I'm sure these need fine-tuning, but I think the community would be able to find what the defaults for the following values should be:

HOLLOW_THRESHOLD
CUT_THRESHOLD
INNER_SHAPE_SCALE

Again, these ought to be changeable on the C# side when we get to that point. For now, there was just an educated guess made as to what that value should be. That may change with future releases.