mod_pubsub_serverinfo: Update to use mod_server_info (fixes #1841) ...but only for Prosody trunk users, because 0.12 mod_server_contact_info does not use the new API in mod_server_info.

--% conflicts: mod_bookmarks
module:log("info", "mod_bookmarks has been deprecated, now loading mod_bookmarks2")
module:depends("bookmarks2")