Tweaks to R_PointToAngle and R_PointToAngle2

Exactly what it says in the title! See commit description for more information on what I did, since I'm too lazy to write it all up a second time. =P

Could someone check that these changes don't cause anything else in particular to go wrong in the game or source code? I haven't checked myself that much yet, mostly because I totally forgot about this thing until now, lol.