SECURITY: Poster IDs could reveal IPs across boards

Imagine the following scenario:

Alice has permission to view IPs on board A, and Bob has permissions to view IPs on board B.

If the post number was to match, and the same IP made both posts, A and B could trade user IPs which they wouldn't normally have permission to do so. This weird bug has already creeped up on 8chan.co and is now patched.
Merge https://github.com/ctrlcctrlv/8chan