base-dirs: add XDG_CONFIG/DATA_DIRS and CONFIGURATION & DATA groups

This adds support for the system-wide locations for configuration and
data files, as defined by the XDG Base Directory Specification.

In addition, it adds two flag groups, CONFIGURATION and DATA, to the
base-dirs system, so that we don't have to hard-code the combinations
of flags everywhere.

modules/module-lua-scripting/module.c

@@ -39,12 +39,8 @@ wp_lua_scripting_package_searcher (lua_State *L)
   const gchar *name = luaL_checkstring (L, 1);
   g_autoptr (GError) error = NULL;
   g_autofree gchar *filename = g_strdup_printf ("%s.lua", name);
-  g_autofree gchar *script = wp_base_dirs_find_file (
-      WP_BASE_DIRS_ENV_DATA |
-      WP_BASE_DIRS_XDG_CONFIG_HOME |
-      WP_BASE_DIRS_ETC |
-      WP_BASE_DIRS_PREFIX_SHARE,
-      "scripts/lib", filename);
+  g_autofree gchar *script =
+      wp_base_dirs_find_file (WP_BASE_DIRS_DATA, "scripts/lib", filename);
 
   if (!script)  {
     lua_pushliteral (L, "script not found");
@@ -142,11 +138,7 @@ find_script (const gchar * script, WpCore *core)
       g_file_test (script, G_FILE_TEST_IS_REGULAR))
     return g_strdup (script);
 
-  return wp_base_dirs_find_file (WP_BASE_DIRS_ENV_DATA |
-                                 WP_BASE_DIRS_XDG_CONFIG_HOME |
-                                 WP_BASE_DIRS_ETC |
-                                 WP_BASE_DIRS_PREFIX_SHARE,
-                                 "scripts", script);
+  return wp_base_dirs_find_file (WP_BASE_DIRS_DATA, "scripts", script);
 }
 
 static void