added r_rtworld, r_rtworldshadows, r_rtdlight, r_rtdlightshadows, and r_lightmapinten...

added r_rtworld, r_rtworldshadows, r_rtdlight, r_rtdlightshadows, and r_lightmapintensity cvars to greatly clean up the handling of the various rtlight/normal rendering modes
ifixed lighting problems on transparent alias models in r_shadow_realtime_world mode with r_shadow_realtime_world_lightmaps < 1 (note: still does not use the rtlights entities, just bsp model light queries like lightmap mode uses)
cleaned up handling regarding RENDER_LIGHT, RENDER_SHADOW, EF_ADDITIVE, alpha, r_fullbright, RENDER_EXTERIORMODEL, and model->flags (now the EF_ADDITIVE and EF_FULLBRIGHT flags were moved to model->flags2)
tag children now inherit RENDER_EXTERIORMODEL from their parent so you can simply attach an external weapon model to the player model and it will appear/disappear according to chase_active appropriately

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@4540 d7cf8633-e32d-0410-b094-e92efae38249