Changed the AI's intercoms around a bit.

West = Custom Channel (mic off, speaker off)
North = Common Channel (mic on, speaker on)
East = Private Channel (mic off, speaker on) //No change

The old system had two intercoms on the common channel, one with the mic on/speaker off and one with the mic off/speaker on. Apparently it was too confusing for players to figure out that when they changed the freq for one, they'd have to change the speaker/mic of the other. Fixes issue 837.

I've also fixed a derp with fire extinguishers I made in my last commit.

git-svn-id: http://tgstation13.googlecode.com/svn/trunk@4548 316c924e-a436-60f5-8080-3fe189b3f50e

code/game/objects/items/weapons/extinguisher.dm

@@ -30,7 +30,7 @@
 	force = 3.0
 	m_amt = 0
 	max_water = 30
-	sprite_name = "mini_FE"
+	sprite_name = "miniFE"
 
 /obj/item/weapon/extinguisher/New()
 	var/datum/reagents/R = new/datum/reagents(max_water)
@@ -47,7 +47,7 @@
 
 /obj/item/weapon/extinguisher/attack_self(mob/user as mob)
 	safety = !safety
-	src.icon_state = "[sprite_name][safety]"
+	src.icon_state = "[sprite_name][!safety]"
 	src.desc = "The safety is [safety ? "on" : "off"]."
 	user << "The safety is [safety ? "on" : "off"]."
 	return