Do not include unnecessary tool_capabilities

This commit makes enchanted tools which have no use for
tool_capabilities to not include it in their metadata.  It does this by
not including tool_capabilities in the metadata of an enchanted tool if
at least one of two cases is true:

(1) The tool is not enchanted with unbreaking or efficiency
(2) The tool does not have tool_capabilities defined in its definition

The first case covers situations like having a pickaxe only being
enchanted with silk_touch.  The second case covers situations like a
piece of armor being enchanted with unbreaking.

mods/ITEMS/mcl_enchanting/enchantments.lua

@@ -770,6 +770,11 @@ mcl_enchanting.enchantments.unbreaking = {
 	description = S("Increases item durability."),
 	curse = false,
 	on_enchant = function(itemstack, level)
+		local name = itemstack:get_name()
+		if not minetest.registered_tools[name].tool_capabilities then
+			return
+		end
+
 		local tool_capabilities = itemstack:get_tool_capabilities()
 		tool_capabilities.punch_attack_uses = tool_capabilities.punch_attack_uses * (1 + level)
 		itemstack:get_meta():set_tool_capabilities(tool_capabilities)

mods/ITEMS/mcl_enchanting/engine.lua

@@ -12,7 +12,7 @@ end
 function mcl_enchanting.unload_enchantments(itemstack)
 	local itemdef = itemstack:get_definition()
 	if itemdef.tool_capabilities then
-		itemstack:get_meta():set_tool_capabilities(itemdef.tool_capabilities)
+		itemstack:get_meta():set_tool_capabilities(nil)
 	end
 	local meta = itemstack:get_meta()
 	if meta:get_string("name") == "" then

mods/ITEMS/mcl_enchanting/groupcaps.lua

@@ -45,12 +45,17 @@ end
 -- To make it more efficient it will first check a hash value to determine if
 -- the tool needs to be updated.
 function mcl_enchanting.update_groupcaps(itemstack)
-	if not itemstack:get_meta():get("tool_capabilities") then
+	local name = itemstack:get_name()
+	if not minetest.registered_tools[name].tool_capabilities then
 		return
 	end
 
-	local name = itemstack:get_name()
 	local efficiency = mcl_enchanting.get_enchantment(itemstack, "efficiency")
+	local unbreaking = mcl_enchanting.get_enchantment(itemstack, "unbreaking")
+	if unbreaking == 0 and efficiency == 0 then
+		return
+	end
+
 	local groupcaps = get_efficiency_groupcaps(name, efficiency)
 	local hash = itemstack:get_meta():get_string("groupcaps_hash")
 
@@ -60,7 +65,6 @@ function mcl_enchanting.update_groupcaps(itemstack)
 
 		-- Increase the number of uses depending on the unbreaking level
 		-- of the tool.
-		local unbreaking = mcl_enchanting.get_enchantment(itemstack, "unbreaking")
 		for group, capability in pairs(tool_capabilities.groupcaps) do
 			capability.uses = capability.uses * (1 + unbreaking)
 		end