2.1.0.1 -> 2.2.0.0: undefined method Loader::library()

Hello there,

I'm trying to upgrade from 2.1.0.1 to 2.2.0.0, basically by copying everything from the opencart-2.2.0.0-compiled/upload folder over the installation and then launching <mydomain>/install

It shows a blank screen and the PHP errors show the following message:

Call to undefined method Loader::library() in /is/htdocs/wp1146543_QK67WBV4H4/www/opencart-2.2.0.0/system/framework.php on line 77

Which is strange, because I've looked into system/engine/loader.php and it does have a public library function. No idea where the problem might be?