Add fancy new feature, which makes "notmuch show" capable of actually
indexing messages that it just decrypted.
This enables a workflow where messages can come in in the background
and be indexed using "--decrypt=auto". But when showing an encrypted
message for the first time, it gets automatically indexed.
This is something of a departure for "notmuch show" -- in particular,
because it requires read/write access to the database. However, this
might be a common use case -- people get mail delivered and indexed in
the background, but only want access to their secret key to happen
when they're directly interacting with notmuch itself.
In such a scenario, they couldn't search newly-delivered, encrypted
messages, but they could search for them once they've read them.
Documentation of this new feature also uses a table form, similar to
that found in the description of index.decrypt in notmuch-config(1).
A notmuch UI that wants to facilitate this workflow while also
offering an interactive search interface might instead make use of
these additional commands while the user is at the console:
Count received encrypted messages (if > 0, there are some things we
haven't yet tried to index, and therefore can't yet search):
notmuch count tag:encrypted and \
not property:index.decryption=success and \
not property:index.decryption=failure
Reindex those messages:
notmuch reindex --try-decrypt=true tag:encrypted and \
not property:index.decryption=success and \
not property:index.decryption=failure