Doomsday Engine

Continued work on map loading and bsp generation:

• Moved the subsector_t builddata into a separate struct: bspleafdata_t which is now only used when building the BSP. Also, reworked things to eliminate the need to store an averaged vertex midpoint in this structure also.
• Moved the redundant map data object checking into edit_map.c (formerly in bsp_analyze.c).
• Moved the logic for determining the sector of a subsector (formerly linkSSecsToSectors()) into hardenLeaf - where the subsector is created.
• Removed the old unclosed sector checking. We now take advantage of the knowledge gained when building the BSP and any unclosed sectors are registered in the process.
• Removed the old linedef missing front checking as a check is now preformed when the linedef is created.
• Removed seg_t->sidedef as it can be determined trivially.
• Further clean up of the BSP code.