liblua: add loader.lua_path

As described previously, loader.lua_path is absolute path where scripts are
installed. A future commit will use this to build paths for dofile in
try_include, rather than the current pcall/require setup that makes it more
difficult to coordinate loader aborts from local.lua -- we do not need the
flexibility of require(), and local.lua is in-fact not a 'module-like' file
as we will not be referencing anything from it.

stand/liblua/lutils.c

@@ -384,6 +384,8 @@ luaopen_loader(lua_State *L)
 	lua_setfield(L, -2, "machine");
 	lua_pushstring(L, MACHINE_ARCH);
 	lua_setfield(L, -2, "machine_arch");
+	lua_pushstring(L, LUA_PATH);
+	lua_setfield(L, -2, "lua_path");
 	/* Set global printc to loader.printc */
 	lua_register(L, "printc", lua_printc);
 	return 1;