Backported Extended ESL Support

It allows older versions of Skyrim to handle files with the new plugin version number. Removes any temptation I might've had to install the update any time soon.

If you reverted to 1.6.640 for example and it was still crashing (as some reported) it's probably because they snuck a new .esl file in that you didn't notice, and this mod should fix that as well.

Even if we never get another Elder Scrolls game worthy of its legacy, Skyrim modding will continue.