Tweaked LLRenderTarget to support depth textures if FBO support is lacking.
Prefer LLRenderTarget::getFBO() over LLRenderTarget::sUseFBO when determining how to handle a specific LLRenderTarget object. (Decoupling to simplify logic without having to track a global)
-Nametag bubble visbility is oddly inconsistent. May vanish with future planned UI merges...
-VBOs are PAINFULLY slow on ATI hardware. This repos self-compiled davep/shining-fixes branch, so I'll leave the ball in LL's court for now regarding that.