[PATCH v2] python: deprecated add_message calls index_file correctly and returns result

[David Bremner]

Gaute Hope <eg at gaute.vetsj.com> writes:

> The deprecated Database.add_message now calls the new index_file with
> correct number of arguments (without an extra `self`), and returns the
> tuple from index_file - as it used to do before.
>
> This change also adds a DeprecationWarning to the function.

Pushed to master, thanks

d