[PATCH v2] cli/show: make --decrypt take a keyword.

[Daniel Kahn Gillmor]

On Mon 2017-12-11 21:33:57 -0500, Daniel Kahn Gillmor wrote:
> We also expand tab completion for it, and update T357 to match.
>
> Make use of the bool-to-keyword backward-compatibility feature.

v2 of this patch just removes an unnecessary attempt to open the
database read-write.  That isn't necessary here, though it will be
necessary if we want to enable future versions of "notmuch show" that
can also interactively add a message to the index.

I removed it from this series so that the interface normalization here
(which is valuable whether or not we decide to augment "notmuch show" as
described) doesn't get distracted by the change.

sorry for the quick revision.

      --dkg