* Using the Doom-style dome here because it looks better.
* this necessitated changes to the backend to allow both types of sky domes at the same time
* do not clamp panning fields for cloudy sky with the new renderer because this makes the texture jump.
* Build skies need a different mesh for the dome - the one from GZDoom distorts them too much.
* made adjustment to the positioning math after redoing the mesh
* Exhumed abuses some strange effect of the original sky placement math which means the y-offsetting must be disabled for this game.
* RRRA sky initialization fixed. It must be done after setting up the tiles.
