generalize creating wrappers for built-ins.

create utility for creating wrapper functions for `minetest` methods.

mods/bg_api/init.lua

@@ -13,4 +13,4 @@ load_file("utils_vector")
 
 load_file("utils_node")
 
-load_file("wrapper_abm")
+load_file("wrappers")

mods/bg_api/wrapper_abm.lua

@@ -1,3 +0,0 @@
-function blockgame.register_abm (...)
-	return minetest.register_abm(...)
-end

mods/bg_api/wrappers.lua

@@ -0,0 +1,20 @@
+local function create_plain_wrapper (function_name)
+	local wrapper = function (...)
+		local args = {...}
+
+		-- labels will be used later, probably.
+		local label = #args > 1 and args[1] or "unlabeled function"
+		local callback = #args > 1 and args[2] or args[1]
+
+		minetest[function_name](callback)
+	end
+
+	blockgame[function_name] = wrapper
+end
+
+for name in pairs({
+	register_abm = true,
+	register_on_joinplayer = true,
+}) do
+	create_plain_wrapper(name)
+end