Doomsday Engine

Continued work on the map loader and BSP generation:

• Revised the algorithm used to detect "one-way windows" to remove use of the glbsp concept of edgetips and instead use the vertex lineowners (not quite the same thing), the edgetips are now used solely by the BSP generator. Also fixed a couple of bugs which had crept in at some point and we now fully support this DOOM.exe trick.
• The vertex lineowner rings are now built early on in the load process.
• Disabled the algorithm used to suppress the creation of segs for overlapping linedefs (typically used for tall mid textures). Our renderer can cope just fine with them present. We now sully support this DOOM.exe trick.
• Orphan subsectors (it's sector cannot be determined as it is degenerate, or all segs are minisegs) can still be produced by the BSP generator under rare circumstances (see Eternall.wad map?). Made various changes within the rest of the engine so that this need not be a critical error and so we can still play maps when they are produced (albeit with possible HOM).
• Removed linked sectors/planes as they were causing just as many rendering problems as they solved.

Now that we have full control over the BSP build process there are much better options available to deal with the numerous self-referencing linedef tricks. I have amassed quite a bit of knowledge in how the various constructs are formed and how DOOM.exe reacts. At a later date we should discus in detail how to handle them the "RightWay" in Doomsday.