Update usages of alpha to the 5.4 convention

mods/ITEMS/mcl_core/nodes_liquid.lua

@@ -7,6 +7,11 @@ local WATER_ALPHA = 179
 local WATER_VISC = 1
 local LAVA_VISC = 7
 local LIGHT_LAVA = minetest.LIGHT_MAX
+local USE_TEXTURE_ALPHA
+if minetest.features.use_texture_alpha_string_modes then
+	USE_TEXTURE_ALPHA = "blend"
+	WATER_ALPHA = nil
+end
 
 local lava_death_messages = {
 	N("@1 melted in lava."),
@@ -36,6 +41,7 @@ minetest.register_node("mcl_core:water_flowing", {
 	sounds = mcl_sounds.node_sound_water_defaults(),
 	is_ground_content = false,
 	alpha = WATER_ALPHA,
+	use_texture_alpha = USE_TEXTURE_ALPHA,
 	paramtype = "light",
 	paramtype2 = "flowingliquid",
 	walkable = false,
@@ -81,6 +87,7 @@ S("• When water is directly below lava, the water turns into stone."),
 	sounds = mcl_sounds.node_sound_water_defaults(),
 	is_ground_content = false,
 	alpha = WATER_ALPHA,
+	use_texture_alpha = USE_TEXTURE_ALPHA,
 	paramtype = "light",
 	walkable = false,
 	pointable = false,

mods/ITEMS/mcl_portals/portal_end.lua

@@ -4,6 +4,11 @@ local S = minetest.get_translator("mcl_portals")
 local SPAWN_MIN = mcl_vars.mg_end_min+70
 local SPAWN_MAX = mcl_vars.mg_end_min+98
 
+local PORTAL_ALPHA = 192
+if minetest.features.use_texture_alpha_string_modes then
+	PORTAL_ALPHA = nil
+end
+
 local mg_name = minetest.get_mapgen_setting("mg_name")
 
 local destroy_portal = function(pos)
@@ -76,7 +81,7 @@ minetest.register_node("mcl_portals:portal_end", {
 	-- This is 15 in MC.
 	light_source = 14,
 	post_effect_color = {a = 192, r = 0, g = 0, b = 0},
-	alpha = 192,
+	alpha = PORTAL_ALPHA,
 	after_destruct = destroy_portal,
 	-- This prevents “falling through”
 	collision_box = {

mods/ITEMS/mcl_portals/portal_nether.lua

@@ -24,6 +24,11 @@ local DESTINATION_EXPIRES = 60 * 1000000 -- cached destination expires after thi
 local PORTAL_SEARCH_HALF_CHUNK = 40 -- greater values may slow down the teleportation
 local PORTAL_SEARCH_ALTITUDE = 128
 
+local PORTAL_ALPHA = 192
+if minetest.features.use_texture_alpha_string_modes then
+	PORTAL_ALPHA = nil
+end
+
 -- Table of objects (including players) which recently teleported by a
 -- Nether portal. Those objects have a brief cooloff period before they
 -- can teleport again. This prevents annoying back-and-forth teleportation.
@@ -140,7 +145,7 @@ minetest.register_node("mcl_portals:portal", {
 	drop = "",
 	light_source = 11,
 	post_effect_color = {a = 180, r = 51, g = 7, b = 89},
-	alpha = 192,
+	alpha = PORTAL_ALPHA,
 	node_box = {
 		type = "fixed",
 		fixed = {