Theme Updater: Current Screen Fix

If we have no theme update transient information and we don't happen to be on the update-core page, we need to tell $this->current_screen that it is an stdClass before assigned the ->base to it
Metabox Saving Fix if multiple tabs

If the user was opening several tabs, one after another, the Sessions variable which holds the "old" data (to see if it has changed before saving it), was holding information from different posts - causing it not to save correctly.

This update attaches the session variable to the post id as well - so that we can open many different posts in many different tabs without overwriting the PHP session variable - causing it to save each post correctly.