Improve slot accessory handling

code/modules/clothing/clothing.dm

@@ -596,12 +596,14 @@ BLIND     // can't see anything
 
 /obj/item/clothing/under/proc/can_attach_accessory(obj/item/clothing/accessory/A)
 	if(istype(A))
-		.=1
+		. = 1
 	else
 		return 0
-	if(accessories.len && (A.slot in list("utility","armband","skullcodpiece","talisman")))
+	if(accessories.len)
 		for(var/obj/item/clothing/accessory/AC in accessories)
-			if(AC.slot == A.slot)
+			if((A.slot in list(ACCESSORY_SLOT_UTILITY, ACCESSORY_SLOT_ARMBAND)) && AC.slot == A.slot)
+				return 0
+			if(!A.allow_duplicates && AC.type == A.type)
 				return 0
 
 /obj/item/clothing/under/attackby(obj/item/I, mob/user, params)

code/modules/clothing/under/accessories/accessory.dm

@@ -7,9 +7,10 @@
 	item_color = "bluetie"
 	slot_flags = SLOT_TIE
 	w_class = WEIGHT_CLASS_SMALL
-	var/slot = "decor"
+	var/slot = ACCESSORY_SLOT_DECOR
 	var/obj/item/clothing/under/has_suit = null		//the suit the tie may be attached to
 	var/image/inv_overlay = null	//overlay used when attached to clothing.
+	var/allow_duplicates = TRUE // Allow accessories of the same type.
 
 /obj/item/clothing/accessory/New()
 	..()
@@ -391,8 +392,8 @@
 	icon_state = "skull"
 	item_state = "skull"
 	item_color = "skull"
-	slot = "skullcodpiece"
 	armor = list("melee" = 5, "bullet" = 5, "laser" = 5, "energy" = 5, "bomb" = 20, "bio" = 20, "rad" = 5)
+	allow_duplicates = FALSE
 
 /obj/item/clothing/accessory/necklace/talisman
 	name = "bone talisman"
@@ -400,8 +401,8 @@
 	icon_state = "talisman"
 	item_state = "talisman"
 	item_color = "talisman"
-	slot = "talisman"
 	armor = list("melee" = 5, "bullet" = 5, "laser" = 5, "energy" = 5, "bomb" = 20, "bio" = 20, "rad" = 5)
+	allow_duplicates = FALSE
 
 /obj/item/clothing/accessory/necklace/locket
 	name = "gold locket"

code/modules/clothing/under/accessories/armband.dm

@@ -3,7 +3,7 @@
 	desc = "A fancy red armband!"
 	icon_state = "red"
 	item_color = "red"
-	slot = "armband"
+	slot = ACCESSORY_SLOT_ARMBAND
 
 /obj/item/clothing/accessory/armband/sec
 	name = "security armband"

code/modules/clothing/under/accessories/holster.dm

@@ -3,7 +3,7 @@
 	desc = "A handgun holster."
 	icon_state = "holster"
 	item_color = "holster"
-	slot = "utility"
+	slot = ACCESSORY_SLOT_UTILITY
 	var/holster_allow = /obj/item/gun
 	var/obj/item/gun/holstered = null
 	actions_types = list(/datum/action/item_action/accessory/holster)

code/modules/clothing/under/accessories/storage.dm

@@ -3,7 +3,7 @@
 	desc = "Used to hold things when you don't have enough hands."
 	icon_state = "webbing"
 	item_color = "webbing"
-	slot = "utility"
+	slot = ACCESSORY_SLOT_UTILITY
 	var/slots = 3
 	var/obj/item/storage/internal/hold
 	actions_types = list(/datum/action/item_action/accessory/storage)