Okay, this is a biggun. Pay attention, everyone.

Moved the handling of P_PlayerInSpecialSector to P_PlayerAfterThink from P_PlayerThink.
* This allows the player to get hurt on sloped lava surfaces that are moving downwards.
* Also prevents the player from standing on death pits for 1 tic.
* Prevents the player moving 1 extra tic's worth of movement of pain when hit by sector.
* Thankfully, no consequences re conveyors.
* Like, the only consequences I've found have been positive. However, this DOES need to be thoroughly investigated before it can be allowed anywhere near Next itself.