This is actually a better solution to the renderer directly accessing
client code than provided by 7e078c7f9c.
Essentially, V_RenderView should not have been calling R_RenderView, and
CL_UpdateScreen should have been calling V_RenderView directly. The
issue was that the renderers expected the world entity model to be valid
at all times. Now, R_RenderView checks the world entity model's validity
and immediately bails if it is not, and R_ClearState (which is called
whenever the client disconnects and thus no longer has a world to
render) clears the world entity model. Thus R_RenderView can (and is)
now called unconditionally from within the renderer, simplifying
renderer-specific variants.
Still, nothing will work: no plugins are loaded and they're all broken
anyway.
glx, sgl, glslx etc are going away, just the basics will be built: fbdev
(probably go away eventually), sdl, x11 and hopefully someday win. That's
actually the only reason anything links.
The renderer should now be free of any direct access to client code. Even
3d rendering is now done via a function pointer.
The cshift code is done as a 2d screen function.
