Renamed Event Variables Backwards Incompatible

https://github.com/phpbb/phpbb/commit/578ee077c114f63a6de0c277669ba91bd9f1219f

The above changes change many event variable names. This is a backwards compatibility breakage for any extensions using them.

If it an be reverted, I think it should. If not, then an announcement to the phpBB community regarding this change should be made.