Add protected-headers="v1" to Content-Type when protecting headers
This is optional part of the draft RFC, marked with "FIXME":
* FIXME: Enigmail adds "protected-headers="v1"" parameter to
"payload" here. Is this necessary?
The answer is: for Enigmail yes. Otherwise it ignores protected headers and use the envelope headers. This results in all the emails listed with "..." subject, which isn't very helpful.