Hello,

Notmuch contains a bit of logic for “normalising” the database path: it can be relative to $HOME and fallsback to $MAILDIR or $HOME/mail. However, this logic is implemented in `notmuch_config_open` and is not available through bindings. So if a third-party tool wants to discover the database, it will either do this incorrectly ([alot]) or will have to roll its own implementation ([afew]). Neither option is good.

Rather than reimplementing it in bindings, I see two possible solutions:

1. Move the logic to `notmuch_database_open` itself.

2. Extract into a separate C function, use it in `notmuch_config_open`, and expose through bindings.

What do you think?

Cheers,

Kirill