A bit of clean up. Moved mod integration lua files to their own folder with a single file designed to check if supported mods are present and load the appropriate local file to setup for it.

mod_integrations/central_message.lua

@@ -0,0 +1,9 @@
+
+function quests.show_message(t, playername, text)
+	if (quests.hud[playername].central_message_enabled) then
+		local player = minetest.get_player_by_name(playername)
+		cmsg.push_message_player(player, text, quests.colors[t])
+		minetest.sound_play("quests_" .. t, {to_player = playername})
+	end
+end
+

mod_integrations/inventory_plus.lua

@@ -0,0 +1,9 @@
+minetest.register_on_joinplayer(function(player) 
+	inventory_plus.register_button(player, "quests")
+end)
+
+minetest.register_on_player_receive_fields(function(player, formname, fields)
+	if (fields.quests) then
+		quests.show_formspec(player:get_player_name())
+	end
+end)

mod_integrations/mod_integrations.lua

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+-- support for several inventory mods
+if minetest.get_modpath("unified_inventory") then
+	dofile(minetest.get_modpath("quests") .. "/mod_integrations/unified_inventory.lua")
+end
+
+if minetest.get_modpath("inventory_plus") then
+	dofile(minetest.get_modpath("quests") .. "/mod_integrations/inventory_plus.lua")
+end
+
+
+--mod that displays notifications in the screen's center
+if minetest.get_modpath("central_message") then
+	dofile(minetest.get_modpath("quests") .. "/mod_integrations/central_message.lua")
+
+else -- define blank function so we can still use this in the code later
+	function quests.show_message(...) end
+end

mod_integrations/unified_inventory.lua

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+unified_inventory.register_button("quests", {
+	type = "image",
+	image = "inventory_plus_quests.png",
+	tooltip = "Show the questlog",
+--	action = function(player)
+--		quests.show_formspec(player:get_player_name())
+--	end
+})
+
+unified_inventory.register_page("quests", {
+	get_formspec = function(player) 
+		local playername = player:get_player_name()
+		local formspec = quests.create_formspec(playername, "1", true)
+		return {formspec = formspec, draw_inventory=false}
+	end
+})
+
+unified_inventory.register_page("quests_successfull", {
+	get_formspec = function(player) 
+		local playername = player:get_player_name()
+		local formspec = quests.create_formspec(playername, "2", true)
+		return {formspec = formspec, draw_inventory=false}
+	end
+})
+
+unified_inventory.register_page("quests_failed", {
+	get_formspec = function(player) 
+		local playername = player:get_player_name()
+		local formspec = quests.create_formspec(playername, "3", true)
+		return {formspec = formspec, draw_inventory=false}
+	end
+})
+
+unified_inventory.register_page("quests_config", {
+	get_formspec = function(player)
+		local playername = player:get_player_name()
+		local formspec = quests.create_config(playername, true)
+		return {formspec = formspec, draw_inventory = false }
+	end
+})
+unified_inventory.register_page("quests_info", {
+	get_formspec = function(player)
+		local playername = player:get_player_name()
+		local formspec = quests.create_info(playername, quests.formspec_lists[playername].list[quests.formspec_lists[playername].id],
+			quests.formspec_lists[playername].taskid, true)
+		return {formspec = formspec, draw_inventory = false }
+	end
+})