[PATCH] forbid atomic transactions on writable, upgradable databases

[David Bremner]

Steven Allen <steven at stebalien.com> writes:

> 1. There is no reason to call `begin_atomic` unless you intend to to
>    write to the database and anyone intending to write to the database
>    should upgrade it first.
> 2. This means that nothing inside an atomic transaction can ever fail
>    with NOTMUCH_STATUS_UPGRADE_REQUIRED.

Applied to master

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