Blender Git Loki

Various fixes:
- Correct fix for file loading crash introduced by earlier point cache commit.
- Simulations are no longer calculated to current frame at render time automatically.
* This has to be thought through more carefully at some point, perhaps through render profiles.
* All simulations can be updated manually to current frame from any cache panel with the "update all to current frame" button.
- Some explanatory comments added for BKE_pointcache.h.