Blender Git Loki

Keyed physics refresh:
- Keyed targets in one list instead of "chaining", this opens up many more possibilities than before and is much less obscure.
- Better keyed timing possibilities (time & duration in frames).
- Looping over keyed targets list.

Other changes:
- New child setting "length" with threshold (great for guard & underfur with a single particle system)
- Modularization of path interpolation code.
- Cleared "animateable" flags from many particle settings that shouldn't be animateable.

Fixes:
- Keyed particles weren't copied properly (ancient bug).
- Hair rotations depended on global z-axis for root rotation so downward facing strands could flip rotation randomly. Now initial hair rotation is derived from face dependent hair matrix. (This caused for example ugly flipping of child strands on some cases).
- Children from faces weren't calculated straight after activating them.
- Multiple disk cache fixes:
* Disk cache didn't work correctly with frame steps.
* Conversion from memory cache to disk cache didn't work with cloth.
* Disk cache crashed on some frames trying to close an already closed cache file.
* Trails didn't work with disk cached particles.
- Child rough effects were effected by emitter object loc/rot making them next to useless with animation, why didn't anybody tell me this!!
- Lots of random code cleanup.