Add another table creation wrapper

I think I really need to figure out how to do this correctly...
Add a "purge" column to IMAP__messages

The idea here is that I don't actually need to have a transaction log,
all I actually need to do is to mark messages to purge on the server
next time a synchronization is performed.

In order to make this work I've added a column to track these sorts of
messages, which later need to be cleaned up by the IMAP
synchronization program later.
Add "rmm", which removes messages

Currently this simply removes a message from the local store and marks
it for purging on IMAP.  Note that I can't yet wake up the IMAP
synchronization thread or actually purge things from IMAP.
Fix synchronization for multiple folders

I wasn't properly initializing the list of messages that exist only on
the server, which was causing messages to be synchronized into
multiple folders.
Make "mh-gmail-watch" be significantly more verbose