Add core event "core.modify_submit_post_data"

Identifier: core.modify_submit_post_data
Location (if applicable): posting.php, right before the submit_post() call.
Explanation: this event allows extensions to modify the whole post data before the post submitting, or even provide its own post submit procedure.
Use case: I have at least 1 extension in development that modifies the post data. The functionality is to glue the current post with a previous one if both has been made by same author.