Bullet 2.1 refactoring in progress: moved and renamed files

[Erwin Coumans]

Currently we are cleaning up Bullet source code for version 2.1

* LinearMath, BulletCollision and BulleDynamics is moved into src folder
* A 'bt' prefix is added to all filenames in BulletCollision and BulletDynamics
* 2 new headerfiles are added in src
* only 1 include folder needs to be added to the project (src), so when using SimdVector3, we include <LinearMath/SimdVector3.h>

todo:
*class method names will uniformly use lowercase
*class names will have the 'bt' like their new filename
* New single C-API headerfile (necessary for Blender project)

See http://www.continuousphysics.com/ftp/pu ... eview2.zip for current status, or http://svn.sourceforge.net/viewvc/bullet/trunk/