Detached signatures for attachments

[barry]

If the user choses to clearsign his message (i.e. signing and not using PGP/MIME), a detached signature should be made for all the attachments.

Originally requested here by Ben Branders

[shane]

I'm not sure about this. A lot of people strip all attachments (Eric, a guy from FreeDOS, does that...as I learned when trying to send him data in the past!). Making signatures seperate attachments seems to open up the possibility of having emails not get through.