Make catwalks behave unsimulated.  Still need to make them suck air from surrounding tiles.

(cherry picked from commit 6ae7a518e552407856d545e230edc4943618d9e9)

Conflicts:
	code/game/turfs/simulated/floor_types.dm
Make catwalks unsimulated.  Fixes #403.

(cherry picked from commit 1c4946b39299d0b736e4759f3e764f5b36801ef0)

Conflicts:
	code/game/turfs/simulated/floor_types.dm
	maps/tauceti.1.1.dmm