Optimize weather effects

[XaserAcheron]

Right now, the rain & snow code is old-DECORATE, and it's using a line-of-sight check to switch itself off, which is rather expensive compared to a distance check (which is more effective anyway, IMO). Either way, it definitely needs to be zscriptified and optimized a bit, especially the snow since H2M4 gets pretty laggy -- I kinda threw that together quickly over a weekend anyway, so it's probably rife with "why did you do that?"-isms. ;)

[Blue-Shadow]

Checking the rain spawner's code, it doesn't appear to use sight checks, only distance checks.

I'll take care of ZScriptifying the rain spawner.

[Blue-Shadow]

Okay, the rain spawner has been ZScriptified (fdb47f5). Testing it in H1M10, I didn't encounter any performance problems.

[XaserAcheron]

Thanks there! Damn, that code is so much better on the eyes. :P

And ye, I misremembered, looks like -- it's just the snow spawners that are using A_CheckSight. That and browsing through H2M4 a bit more, it's definitely more the volume of snow particles that's the culprit, rather than the spawners being troublesome. I'll need to play around with the 'particle' lifetimes and try a few different spawning techniques to cut down on the amount of lingering snowflakes everywhere.