[Bf-python] Minimalist "set" built-in type for blender w/Python 2.3?

[Ken Hughes]

I started looking over old code I'd worked on which added tp_getset 
access to sceneRender.c, and in the process it reminded me of something 
else which I wanted to do.  I'm cringing each time I add something new 
to the API which uses bitmask/bitfields, knowing we don't want to do it 
this way in the new API.

We'd discussed using the set built-in which was added to in Python 2.4, 
but since we need to still be backward compatible with 2.3 I was 
thinking about implementing a minimalist set built-in type which would 
only be compiled into Blender running Python 2.3 (which Stephen also 
tells me should only be needed on Windows since it's assumed all other 
OSes have python installed).

I figure it's either write this now and then implement access to 
bitfields right now (and throw this built-in away when we scrap 2.3), or 
  go back and have to re-write the access in the new modules later along 
with everything else.  So in my mind, it would be less work to do this 
in the long run.

If anyone thinks this is a really bad idea, then tell me now before I 
spend time trying to do it.  If anyone thinks it's a really good idea, 
then also tell me now so I can get started.

If this seems like a good idea, what methods and operators must be 
supported?  Remember, the intent is to allow manipulation/access to 
Blender bitfields, not for general-purpose usage.

Ken