Add collision to southern wall

[csclyde]

it seems that the southern wall has no collision data. also, the northern wall should have its collision drawn up a little bit, so you it looks like half your torso can go in front of the wall.

[lyleunderwood]

i actually lowered the northern wall so that the alcove would be nice and spacey for them to spawn in. i suppose i could make it smaller if we feel that's the way to go.