Blender Git Loki

SPH particle simulation 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.