*** These files in extern/bullet2 are NOT part of the Blender build yet *** This is the new refactored version of Bullet physics library version 2.x Soon this will replace the old Bullet version in extern/bullet. First the integration in Blender Game Engine needs to be updated. Once that is done all build systems can be updated to use/build extern/bullet2 files. Questions? mail blender at erwincoumans.com, or check the bf-blender mailing list. Thanks, Erwin