Don't fail if virtualtilesets.vts doesn't exist.
BuildingEd: Added "shallow" roof caps and slopes.
BuildingEd: Cleaned up the roof-corner-tile code.
Ported BuildingMap fixes from TileZed.
Rewrote heightmap view to use TextureMgr and VirtualTilesetMgr stuff.
Ported QGLPixelBuffer bug work-around from TileZed.
HeightMapScene: Ensure all lots are loaded before loading textures.

Should use the same code as DelayedMapLoader...
Removed old renderWallTiles() code from HeightMapItem.
Clean up heightmapview.cpp a bit.
Changed dist.tcl for Qt 5.1.1