Atmospheric effects don't work correctly in split-screen

[zturtleman]

The Wolfenstein: Enemy Territory atmospheric effects (rain and snow) in split-screen run too fast and rendered particles for all local players leading to "high density" areas around other local players being visible from a distance. There is some other flickering issues.

I have a possible solution at https://github.com/zturtleman/mint-arena/compare/atmfx-splitscreen but I'm still thinking about it.

Reported by Tobias Kuehnhammer.