[Bf-taskforce25] Using hash tables for ID block lookup

[joe]

I had an idea; we should maintain hash tables for each ID type.  These
hash tables would be maintained entirely at runtime (and of course
would not be written to disk), and would be used to lookup ID blocks
by name.  We all know blender has problems with many ID blocks in a
file, and I think this would go a long way towards solving them.  It'd
may also give a big speed boost to f-curves, especially scene-level
f-curves (for example, from scene actions).

Joe