2.5.1

• More sanity checking for invalid P2P connection types.
• Avoid a PHP notice when a query uses orderby without order.
• Add a caching wrapper for column generation, as this gets called multiple times on a post listing screen.
• Add a caching wrapper for p2p_connection_exists() which gets called multiple times and which performs a database query on every call.
• Implement post type labels introduced in WordPress 4.4.