This allows MUAs that don't want to think about per-mime-part
cryptographic status to have a simple high-level overview of the
message's cryptographic state.
Sensibly structured encrypted and/or signed messages will work fine
with this. The only requirement for the simplest encryption + signing
is that the message have all of its encryption and signing protection
(the "cryptographic envelope") in a contiguous set of MIME layers at
the very outside of the message itself.
This is because messages with some subparts signed or encrypted, but
with other subparts with no cryptographic protection is very difficult
to reason about, and even harder for the user to make sense of or work
with.
For further characterization of the Cryptographic Envelope and some of
the usability tradeoffs, see here:
https://dkg.fifthhorseman.net/blog/e-mail-cryptography.html#cryptographic-envelope
The current behaviour is at best under-documented. The modified test in
T470-missing-headers.sh previously relied on printf doing the right
thing with NULL, which seems icky.
The use of talloc_strdup here is probably overkill, but it avoids
having to enforce that thread->authors is never mutated outside
_resolve_thread_authors_string.
Instead of just having the first filename for the message, list all
duplicate filenames of the message as a list in the formatted
outputs. This bumps the format version to 3.
The files (test) scripts source (with builtin command `.`) provides
information which the scripts depend, and without the `source` to
succeed allowing script to continue may lead to dangerous situations
(e.g. rm -rf "${undefined_variable}"/*).
At the end of all source (.) lines construct ' || exit 1' was added;
In our case the script script will exit if it cannot find (or read) the
file to be sourced. Additionally script would also exits if the last
command of the sourced file exited nonzero.
All test scripts to be executed are now named as T\d\d\d-name.sh,
numers in increments of 10.
This eases adding new tests and developers to see which are test scripts
that are executed by test suite and in which order.
