C02 -> carbon_dioxide

Renamed carbon dioxide breathing type string to hopefully prevent
confusion in the future.

code/modules/mob/living/carbon/human/life.dm

@@ -460,7 +460,7 @@
 				inhaling = breath.nitrogen
 			if("phoron")
 				inhaling = breath.phoron
-			if("C02")
+			if("carbon_dioxide")
 				inhaling = breath.carbon_dioxide
 			else
 				inhaling = breath.oxygen
@@ -470,13 +470,13 @@
 				poison = breath.oxygen
 			if("nitrogen")
 				poison = breath.nitrogen
-			if("C02")
+			if("carbon_dioxide")
 				poison = breath.carbon_dioxide
 			else
 				poison = breath.phoron
 
 		switch(species.exhale_type)
-			if("C02")
+			if("carbon_dioxide")
 				exhaling = breath.carbon_dioxide
 			if("oxygen")
 				exhaling = breath.oxygen
@@ -521,7 +521,7 @@
 				breath.nitrogen -= inhaled_gas_used
 			if("phoron")
 				breath.phoron -= inhaled_gas_used
-			if("C02")
+			if("carbon_dioxide")
 				breath.carbon_dioxide-= inhaled_gas_used
 			else
 				breath.oxygen -= inhaled_gas_used
@@ -534,7 +534,7 @@
 					breath.nitrogen += inhaled_gas_used
 				if("phoron")
 					breath.phoron += inhaled_gas_used
-				if("C02")
+				if("CO2")
 					breath.carbon_dioxide += inhaled_gas_used
 
 		// Too much exhaled gas in the air

code/modules/mob/living/carbon/species.dm

@@ -19,7 +19,7 @@
 
 	var/breath_type = "oxygen"   // Non-oxygen gas breathed, if any.
 	var/poison_type = "phoron"   // Poisonous air.
-	var/exhale_type = "C02"      // Exhaled gas type.
+	var/exhale_type = "carbon_dioxide"      // Exhaled gas type.
 
 	var/cold_level_1 = 260  // Cold damage level 1 below this point.
 	var/cold_level_2 = 200  // Cold damage level 2 below this point.