Changed how polygonbegin guesses if the geometry is 2D or 3D, it now uses a separate...

Changed how polygonbegin guesses if the geometry is 2D or 3D, it now uses a separate variable rather than relying on r_refdef.draw2dstage.

Reworked DrawQ_* and R_RenderView code to make clear distinctions between 2D and 3D code, this removes a lot of unnecessary calls to DrawQ_FlushUI (including ones that happened in R_RenderView).

Added R_DebugLine which takes a line in world coordinates and adds it as a 2D line in CL_Mesh_UI.

Added r_showparticleedges and r_showspriteedges debugging cvars which make use of R_DebugLine.

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@12397 d7cf8633-e32d-0410-b094-e92efae38249