Blender Git Loki

Added a cache library pointer to objects as a replacement for CL->GR
pointers.

Relationship between CacheLibrary, duplicator Objects and Groups is
difficult. There are a number of somewhat conflicting goals:
- CacheLibraries write out data for objects and dupli groups. Multiple
objects can be stored in the same cache: CL *->* GR
- Objects can override a dupli group with different caches: OB *->1 CL
- As before, each object can be the duplicator for one group: OB *->1 GR

To combine these requirements, the first relationship will be made
indirect. Only the Object -> Group/CacheLib relations are explicit
pointers in the DNA. For finding all objects contained in a cache
library the usual recursive DNA tagging system must then be used.