From the newsgroup: traps created on the location of dug out vault
walls would be left in place when/if the vault guard repaired the walls.
Since known traps get precedence over walls when drawing the map, this
produced a display oddity in addition to the topological one.
It also appears that monsters in affected spots wouldn't be handled
correctly if they happened to be in a direct horizontal or vertical line
with the guard. I don't know whether that matches any of the assorted
unresolved old vault bugs.
This eliminates a chunk of redundant code by merging two loops.
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