Plane displacement
Basic support for plane displacement, no netplay support as of writing but this is what Nev3r wanted moreorless at least.
Linedef types 66-68 are the plane displacement specials; 66 = move floor only, 67 = move ceiling only, 68 = both
Front sector = control sector
Tag = tag of target sectors to be moved whenever the control sector floor moves
Linedef length = movement factor relative to control sector movement, 256 = 1:1 with control sector. 128 is half as much, 512 is twice as much, etc.
Whenever the control sector floor moves (not ceiling, never ceiling), the selected planes of the tagged sectors all move (mind, they have a tic delay due to how it all works, it's not perfect really). No support for reverse speeds yet sorry.
EDIT: oh, btw, test exe and test map are included in my folder on the FTP (srb2win-plane-displacement.exe and plane-disp-test.wad, respectively)
See merge request !61
* Only change texture when stationary or moving down, for additional fidelity to source material. This has zero overhead, and actually might REDUCE lag in some circumstances... my nitpickiness wins again.
* Apply ML_EFFECT1 to it to make it invisible and intangible (removing (FF_SOLID|FF_RENDERALL|FF_CUTLEVEL) from it) from every side except the bottom. Becomes visible and tangible when it's hit once. Might fuck over players in mp, but really our Mario blocks are so high in the air (and we'd need to update Pipe Towers to take advantage anyways) that they're super unlikely to get a kill this way
* Checks for the Brick Block have been switched over to the presence of FF_SHATTERBOTTOM instead of checking for the source linedef's flags every time.
