Line_AlignCeiling

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184:Line_AlignCeiling (lineid, side)

lineid: Line to use for alignment 
side: Align sector in front of or behind the line? 

Causes the tops of the ceiling textures in the front (0) or back (1) of the specified line to align with the line. Any future scrolling or rotation of the ceiling will use this new alignment as a basis, unless changed again with one of these specials. The reason for this is so that once rotating sectors are a reality, you only need to align the texture once, and it will stay aligned as you rotate the sector.