Realised I accidentially broke rain in the rainfixes branch (oh, the irony!),...

Realised I accidentially broke rain in the rainfixes branch (oh, the irony!), realised it needed a few additional P_RecalcPrecipInSector calls to properly work with the new arena, and increased its speed.

If you must, I can cherrypick this into another branch - but it's required for this one, at least.