* 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.
This was by far the messiest game, there's two reasons for this.
First, the portal links do not need to be in an actual portal sector, so they cannot be used to detect portal sectors.
Second, the game moves portals in place, so all offsets are (0,0,0) so that not even these can be used for detection.
The only working method is the super-complicated original way to look up portals at run time, just being done at map start.
Having static portal links should reduce the render glitches quite significantly because the renderer knows now which sectors belong to a portal and can use this information to ensure proper processing.
Unlike the other games these are so poorly defined that the engine has to rely on the original fudging to pick the proper portal to link to. As a result they are just as limited as they always were.
In addition all the portal search code had to be reinstated.
Note that these portals cannot be rotated, so to preserve bad setups this limitation needs to be replicated.
If we want proper line to line portals for all games they need to be made a different portal type.
