Allow users to delete own posts even if not the last post in a topic

Please let us know if this should be discussed in the phpBB forums instead, not quite sure if this is the right place. We do intend to implement this ourselves, but hope to submit back to the project.

Right now, phpBB allows regular users to soft delete their own posts, but only if it's the last post in the topic. The goal of this ticket is to allow admins to choose whether to keep phpBB's default behavior, or allow users to soft delete any of their own posts, regardless of whether it's the last post in a topic or not.

Our proposal:

• modify functions_posting.php, phpbb_handle_post_delete() so that it only checks if the post ID is equal to the topic's last post ID if admins have set a specific config value;
• add a new site-wide config value in the ACP that sets whether the forum should restrict post deletion to the last topic post or not.

The default would remain the current behavior of not allowing users to delete a post unless it is the last post in a topic. This would just allow us the option to override this behavior.