Fix crash and confusing behavior in automaterial.
Enabling designation like rectangular selection for constructions, with unlimited selection size and auto skipping of tiles that can't be built on.
Improved check for figuring out what tiles can have constructions.
Better handling of open space construction placement
Allow placing constructions in unconnected open space, with sensible restrictions
Make gcc happy
Allocate sky blocks when needed.
Allow stairs to be designated on top of each other in open space.
Merge branch 'automaterial' of https://github.com/Falconne/dfhack into automaterial_box
Merge branch 'automaterial_box'