This patch fixes a number of bugs in the SPH simulation code:

Basic fixes:
- Using correct frame to update particle system tree for SPH simulation (i.e. psys_update_particle_bvhtree(psys, cfra)).
- Increased SPH neighbour count to 512 - this greatly reduces BVH tree search bias, and makes simulations more symmetrical.

Adaptive time step improvements:
- Fix for relative velocities based on previous state (fixes fast-moving particle clusters).
- Only reporting on element size once per time step. Prevents incorrect Courant number from being calculated when using multiple-step integration.

Refactor: Moved per-particle courant calculation into a separate function. This cleans up the code, and makes it possible to reuse it for other solvers in future.

Test files: use the files that were attached to the original adaptive time step patch.
http://projects.blender.org/tracker/?group_id=9&atid=127&func=detail&aid=27442