Blender Git Loki

Fixes for scons build files.

Fix for circular linker dependency with cache code library.

The `bf_pointcache_alembic` code is a separate library, to avoid
muddling up core code with alembic includes and preprocessor defines.
Alembic stuff only belongs strictly into alembic code and can be
disabled cleanly.

The `bf_pointcache` and `bf_pointcache_alembic` libraries had a circular
dependency, because the alembic implementation functions were called
directly. Now there is a "Factory" class to abstract the creation of
concrete implementations for readers and writers.
`bf_pointcache_alembic` defines this factory and is registered
//outside// of the core `bf_pointcache` lib, so there is no linker
circularity.

Removed unused thread mutex file from pointcache lib.

Removed deprecated rna_pointcache.c file.

Scons was still compilling this, since it's source files are not
explicit.

Fix for indirectly linked object pointers in cache libraries.

These must be made "extern" to avoid losing links on loading.

Removed remaining 1 frame difference in archive storage.

This was an artifact from the previous way of mapping non-0 start frame
to time 0.0. Now we start at times > 0.0 to match with the start frame.
Both ways are possible, can be changed later if needed.

Fixed start frame mapping in Alembic archives.

Writers were always starting at time 0.0, which means that for start
frames > 1 the readers would always be off. Now match the writer start
frame to the actual Blender start frame.

Added poll function for the cache manager panel to prevent hiding in
Cycles render engine.

The "compat_engines" thingy really gets in the way here ...

Cache reading for particle paths.

Fix for cache modifier linking and handling of the default case (no
cachd modifier).

Changed implementation of the Cache modifier to work in tandem with the
cache library system.

The Cache modifier is now an optional "break point" of the modifier
stack:
- Without a cache modifier the stack works as before. Baking will write
the final stack result. After baking the cache replaces the whole
stack.
- With a cache modifier the stack result at the modifier's position is
stored. The cache is then applied as the output of that modifier,
skipping preceding modifiers. That way additional modifiers can be
applied on top of the cache.
- When using multiple cache modifiers, only the last (active) one will
be used, since all previous cache results would be discarded anyway.

Replaced point cache in cloth modifiers (also hair) with the new caching
system.

'expand' function for cache libraries, so link/append makes it load the
group and objects too.

Make cache libraries a linkable data block.

Take NULL object pointers in cache items into account.

This can happen if an object gets deleted or isn't loaded for some
reason. The item should just be ignored in that case and removed at the
next opportunity (cleanup function).

When using the "new cache library" operator, enable fake user by
default.

Nothing actually links to a cache library at this point (and probably
won't in the future), so fake user is necessary to avoid losing data.

Display cache library name and fake user button, imitating template_ID.

Importing of caches into Blender data.

Currently only implemented for DerivedMesh.
This replaces the `final_dm` calculation of the modifier stack with the
result from cache loading.

UI fixes, draw bake operator button only once at the top.

Hair path writer needs 2 different variants for parent/child hairs.