Updated Blender's Bullet to 2.76 in this branch only.
This update was done by:
1) deleting the contents of the existing extern/bullet2/src directory (leaving the .svn folder in place),
2) copy/pasting the contents of the bullet/src directory (from unzipped Bullet archive) into this newly cleared folder.
Hopefully there aren't any patches that are still needed from the Bullet we had in source.
---
Note: I didn't use Moguri's patch, since that was giving me compile errors with headers not being able to be found.
[[Split portion of a mixed commit.]]
