[ticket/12927] core.mcp_queue_get_posts2_query_before

Adding the core.mcp_queue_get_posts2_query_before event to mcp backend.

https://tracker.phpbb.com/browse/PHPBB3-12927

PHPBB3-12927
I expected that :).
I just don't have any ideas about this because the other name that was related to this was was requested to be changed. This is a copy of the final name that was decided for the other related event but with a 2. That's because both (from that restricted naming) *do the* exact *same* :S.