include attachments in forwarded message - detached

[tomholub]

customer request

[DenBond7]

@tomholub I've added support for forwarding detached attachments. Detached should be read as a part of the MIME message(MIME part with Content-Disposition: attachment;). But we still do not support forwarding inlined encrypted attachments. It will be for a separate issue and it will not be so easy as the current issue :(

[tomholub]

The terminology is a bit confusing, as pgp/inline normally comes with detached signatures (which is what you support) whereas pgp/mime has attachment encoded in it. It could be inline images but generally they are not. Let me rename the issues.