Another question - backing up the address book. How do I do that. Couldn't find an obvious address book file.
The address book is, uh... in messages.dat. Don't ask me why.
As for upgrading with git, you can "pull" or you can "fetch" and "merge."
Oh, that's a GREAT place to put the address book.
It also holds other people's public keys, the network object inventory, your subscriptions, and your whitelist and blacklist. So it is reasonably logical that it would also hold your address book.
And possibly a way to access and import addresses directly from the address book in the "Send" dialogue? This way I don't have to switch tabs and copy+paste manually.
Right click on one or more addresses in your address book and "Send message to this address".
OperationalError: database is locked
A quick google search suggests that you should restart your computer because some process besides Bitmessage might have a lock on the database.