[sldev] Small Prim Culling

[Jason Giglio]

Anna Gulaev wrote:
> LLVolumeGeometryManager::rebuildGeom? That's where facep->mPixelArea is 
> compared to FORCE_CULL_AREA and FORCE_SIMPLE_RENDER_AREA, anyway. 
> Grepping the code for PixelArea seems to turn up where it's calculated.
> 

I don't think that's it, because this small prim culling happens based 
on where your agent is standing, not where your camera is.  So an object 
that covers your entire screen in pixel area can still disappear.

-Jason