some terrain tweaks

Walkway(t_bridge) gets "flat" flag
Breaking boarded window will create some glass shards
Empty window doesn't have "barricadable_window" flag anymore
New terrain : "t_window_boarded_noglass"

adding missing ","
some construction tweaks

Can fill spiked pits(t_pit_spiked)
Boarding up empty window will create "t_window_boarded_noglass" instead of "t_window_boarded"