Bullet 2.75 beta1: GPU, SPH fluids preview, new constraints

[Stefan]

Bullet 2.75 beta 1 (SVN revision 1676) is available for download and testing:
http://code.google.com/p/bullet/downloads/list

Some features:

    * Smoothed Particle Hydrodynamics (SPH) fluids preview, thanks to Rama Hoetzlein for contributing this under the ZLib license! See Bullet/Extras/sph. The SPH fluids will be integrated into Bullet with two-way interaction, similar to cloth/soft body simulation.
    * GPU physics kernels preview. Right now mainly CPU version, you can enable CUDA version manually. An OpenCL version will follow soon. See Bullet/Demos/Gpu2/3dDemo
    * 2D physics demo, with 2D and 3D object interaction, see Bullet/Demos/Box2dDemo
    * New constraints: btHinge2Constraint,btUniversalConstraint,btGeneric6DofSpringConstraint, thanks to Roman Ponomarev
    * Use ALT+Left/Middle/Right Mouse button+mouse motion for Maya-style camera navigation
    * many bug fixes