Adds support for inverse required temp reactions.

Ie. Cooling a mixture to cause a reaction, instead of heating it. Just
set 'is_cold_recipe' to 1 in the reaction.

code/modules/reagents/chemistry/holder.dm

@@ -344,6 +344,7 @@ var/const/INJECT = 5 //injection
 				var/matching_other = 0
 				var/list/multipliers = new/list()
 				var/required_temp = C.required_temp
+				var/is_cold_recipe = C.is_cold_recipe
 
 				for(var/B in C.required_reagents)
 					if(!has_reagent(B, C.required_reagents[B]))
@@ -377,7 +378,7 @@ var/const/INJECT = 5 //injection
 					required_temp = chem_temp
 
 
-				if(total_matching_reagents == total_required_reagents && total_matching_catalysts == total_required_catalysts && matching_container && matching_other && chem_temp >= required_temp)
+				if(total_matching_reagents == total_required_reagents && total_matching_catalysts == total_required_catalysts && matching_container && matching_other && (is_cold_recipe ? chem_temp <= required_temp : chem_temp >= required_temp))
 					var/multiplier = min(multipliers)
 					for(var/B in C.required_reagents)
 						remove_reagent(B, (multiplier * C.required_reagents[B]), safety = 1)

code/modules/reagents/chemistry/recipes.dm

@@ -13,6 +13,7 @@
 	var/mob_react = 0 //Determines if a chemical reaction can occur inside a mob
 
 	var/required_temp = 0
+	var/is_cold_recipe = 0 // Set to 1 if you want the recipe to only react when it's BELOW the required temp.
 	var/mix_message = "The solution begins to bubble." //The message shown to nearby people upon mixing, if applicable
 	var/mix_sound = 'sound/effects/bubbles.ogg' //The sound played upon mixing, if applicable