-Codechange: missing space (yes, those things annoy me)
-Codechange: use enums for structuresRequired  (based on patch by wangds)

FLAG_STRUCTURE_NEVER is a bit special, but by the lack of a better name
it will have to do.
-Fix: forgot to add doxygen comments where needed
-Codechange: use enums for availableHouse (patch by wangds)