The final breath of _bsp_subdivide()

I wrapped up a series of horrible, terrible, ugly hacks into
bsp_clip_polygons() to translate klist_t(poly) lists into
poly **arrays, with massive duplication just to kill
the old subdivide function.

At least now we can be on an even footing.
Leave the party early if there's no one left.
Merge pull request #16 from sshirokov/array_subdiv_in_clip

Remove the klist_t(poly) backed bsp_subdivide()