This is something that should never be done!!
It will make your mouse-speed fps-dependent, meaning that with very low fps you can only turn the camera/player very very slow. If you don't belive me, try it out.
No game does this, and it's for a reason.
You're right, i thought it would be the same as with the player movement. Normally the time_step var makes things fps-independent, actually in this case its the opposite way around.
