Rewrote bouncegrid path splatting, it now has a cone shape which grows with distance...

Rewrote bouncegrid path splatting, it now has a cone shape which grows with distance, which reduces the splotchy look (cvars r_shadow_bouncegrid_lightpathsize_initial and r_shadow_bouncegrid_lightpathsize_conespread control this).

Replaced r_shadow_bouncegrid_(static|dynamic)_energyperphoton with r_shadow_bouncegrid_(static|dynamic)_quality cvar which works opposite the old one and is automatically multiplied by spacing^2 so you no longer have to hand-tune it when changing spacing.

Turned off r_shadow_bouncegrid_blur by default - it's still useful but no longer completely necessary.

Replaced r_shadow_bouncegrid_dynamic_stablerandom with r_shadow_bouncegrid_rng_type (which defaults to Lehmer 128bit RNG) and added r_shadow_bouncegrid_rng_seed (which can be set to -1 for the time-based random that stablerandom <= 0 used to trigger).

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@12304 d7cf8633-e32d-0410-b094-e92efae38249