Blender Git Loki

Refactoring of archive handling in readers/writers.

Now instead of each reader/writer creating its own archive, the archive
is created by the caller in advance and passed as a constructor
argument. This means that multiple items can be stored together in the
same archive.

General support for export to/import from Alembic files based on Cache
Libraries.

Name string construction for cache items, to use as a unique identifier
in the cache library.

Deleted unimplemented parts of the previous pointcache system, to make
refactoring simpler.

Since the new approach is not tied to the old set of point cache data
types there is really no need to carry their empty husks around. Once
the new caching system is defined in detail we can add back whatever
makes sense.

Unlink and cleanup functions when objects or the cached group get
unlinked or changed.

Fix for undefined return value.

Removed unused Scene pointer from the base Reader/Writer classes.

Operator skeleton for a cache bake operator, using the job system.

Disabled specialized Point Cache modifier handling in the modifier
stack, this will be replaced and is not correct anyway.

Removed unused line.

Make sure cache item pointers are lib-linked correctly.

Link main CacheLibrary pointers in readfile.

Simple cache manager panel UI in the scene buttons.

This is mostly a simple and unintrusive placeholder to have some way of
making caches accessible, but needs some more thought.

Missing include.

New ID datablock 'CacheLibrary', for managing physical cache archives
and files.

At it's core this is just a file path, but many different cache users
may refer to this, so having a dedicated ID block helps. It can be
compared to Image datablocks, which also primarily are used for data
on storage, but can be packed with the blend file, and carry some
additional information that would be cumbersome to keep sync'ed
otherwise.

The name 'CacheLibrary' deliberately resembles the 'Library' datablock:
just as a Library stores ID blocks in a physical file, a CacheLibrary
stores cached data (in Alembic HDF5/Ogawa or other formats).

Conflicts:
source/blender/blenkernel/BKE_pointcache.h
source/blender/blenkernel/intern/pointcache.c
source/blender/makesdna/DNA_pointcache_types.h

Conflicts:
source/blender/makesrna/intern/rna_main_api.c

BKE functions for managing cache content based on a group.

This uses a complete hierarchy of group instances, based on a path
hierarchy (object names).

Putting

Updated hash table for lookup of enabled cache items and added basic
UI support.

Improved collections in RNA for looping over potential caching items
in the object group.

Removed meaningless comment.

Simplified cache item path description, based on plain ID blocks with
subtype/index.

This omits possible instancing and recursion by dupli groups, but since
the data of instances is always the same in Blender at this point, there
is little need to take them into account for caching.

At some point in the future it may become desirable to store full dupli
hierarchies in the cache, but it doesn't make sense to try to design a
fully-fledged path descriptor for this hypothetical case now.