Allow shorter module name specification in wesnoth.require

Basically, you can now omit the "lua/" prefix and the ".lua" suffix.
If necessary, they will automatically be applied for you.

data/lua/package.lua

@@ -1,14 +1,35 @@
 
 local empty_pkg = {}
 
+local function resolve_package(pkg_name)
+	if wesnoth.have_file(pkg_name) then return pkg_name end
+	if pkg_name:sub(-4) ~= ".lua" then
+		if wesnoth.have_file(pkg_name .. ".lua") then
+			return pkg_name .. ".lua"
+		end
+		if pkg_name:sub(1, 4) ~= "lua/" then
+			if wesnoth.have_file("lua/" .. pkg_name .. ".lua") then
+				return "lua/" .. pkg_name .. ".lua"
+			end
+		end
+	end
+	if pkg_name:sub(1, 4) ~= "lua/" then
+		if wesnoth.have_file("lua/" .. pkg_name) then
+			return "lua/" .. pkg_name
+		end
+	end
+	return nil
+end
+
 function wesnoth.require(pkg_name)
 	-- First, check if the package is already loaded
-	if wesnoth.package[pkg_name] then
-		return wesnoth.package[pkg_name]
+	local loaded_name = resolve_package(pkg_name)
+	if loaded_name and wesnoth.package[loaded_name] then
+		return wesnoth.package[loaded_name]
 	end
 
 	-- Next, load the package with dofile
-	local pkg = wesnoth.dofile(pkg_name)
-	wesnoth.package[pkg_name] = pkg or empty_pkg
+	local pkg = wesnoth.dofile(loaded_name)
+	wesnoth.package[loaded_name] = pkg or empty_pkg
 	return pkg
 end