Committing with serious memory problems. Valgrind is a little bit
helpful. Basically, at the end of
DungeonBuilder::determine_which_wall(), the Room vector in the Dungeon
object gets entirely thrown out. Valgrind also detects an "invalid read
of size 8" there. If you hate me for this, you can just revert to the
last commit and go from there, and I'll fork this one and work on it.