Add signature verification of PGP/MIME-signed parts with --verify.

This is primarily for notmuch-show, although the functionality is
added to show-message.  Once signatures are processed a new
part_sigstatus formatter is emitted, and the entire multipart/signed
part is replaced with the contents of the signed part.

At the moment only a json part_sigstatus formatting function is
available.  Emacs support to follow.

The original work for this patch was done by

  Daniel Kahn Gillmor <dkg@fifthhorseman.net>

whose help with this functionality I greatly appreciate.

1 files changed, 11 insertions, 0 deletions

diff --git a/notmuch.1 b/notmuch.1
index a1c7fa8..daa9c6f 100644
--- a/notmuch.1
+++ b/notmuch.1
@@ -321,6 +321,17 @@ a depth-first walk of the message MIME structure, and are identified
 in the 'json' or 'text' output formats.
 .RE
 
+.RS 4
+.TP 4
+.B \-\-verify
+
+Compute and report the validity of any MIME cryptographic signatures
+found in the selected content (ie. "multipart/signed" parts). Status
+of the signature will be reported (currently only supported with
+--format=json), and the multipart/signed part will be replaced by the
+signed data.
+.RE
+
 A common use of
 .B notmuch show
 is to display a single thread of email messages. For this, use a