OptiFine fast fog is denser and fancier than it should be

[makamys]

Just a small oddity I noticed while testing stuff. The fog shader doesn't support fast fog, so when OptiFine's fog is set to fast (which is the default), it results in noticeably denser fog than without OF.

When the fog is set to fancy, everything works as expected.

Fog/Mods	Fast fog	Fancy fog
Vanilla / Nd	N/A
OF
OF + Nd