Shutters and poddoors now crush.

Fixes #661, does the same as #821 but better.

Instead of having a loop for airlocks, crush() is now a function of /obj/machinery/door. It's called when airlocks and poddoors close (shutters are a subtype of poddoors, so it's not needed there.)

Other than that, looking at the code, I think some blood would've been spawned when a cyborg was crushed, so I fixed that, too.

Sorry about the ton of other commits I really need to start using branches. :cry: