The Django haystack update_index job needs a way to do a single list.

When importing archives, the imported messages aren't indexed for searching. The Django runjob update_index job which is run minutely only does new messages by date and doesn't do older imported messages. The Django update_index job does the whole site and takes several hours for 60K messages. We need a way to update the index for all the messages in a single list so we can import its archives and index them without doing the whole site. This may require haystack modification, but possibly we can do it with just a new HyperKitty job.