Cleaned up and moved some more rendering code from com.mojang.minecraft.Minecraft into com.mojang.minecraft.render.Renderer: setCamera(...) and drawWeather(...)
Added "isOpaque" field to GuiScreen, to allow skipping the level-rendering path on level-generation, level-loading, and error screens. Also renamed Minecraft.isOnline to Minecraft.isConnecting. Also cleaned up Renderer.drawWeather(), and added some comments.
Prevented level from rendering under the opaque disconnect/kick/error GUI screens, to avoid wasting CPU/GPU resources. Also: commenting, renaming vars, removing unused imports.