v4 of legacy-display cleanup

[David Bremner]

Daniel Kahn Gillmor <dkg at fifthhorseman.net> writes:

> This is the fourth revision of the series that cleans up legacy-display
> protected headers parts so that notmuch users only have to look at one
> subject line.
>
> version 3 can be found at id:20190625014107.12452-1-dkg at fifthhorseman.net
> version 2 can be found at id:20190531075907.17035-1-dkg at fifthhorseman.net
> version 1 can be found at id:20190531042825.27774-1-dkg at fifthhorseman.net
>
> ----------
> Now that notmuch can handle and interpret protected subject lines, it
> should also avoid forcing the user to look at "legacy display" parts
> that some MUAs (notably enigmail) copies of the protected headers that
> are intended to be rendered only by legacy clients -- clients capable
> of decryption but which don't understand how to handle protected
> headers.
> ----------

series pushed to master

d