Bug 2977

When claws sends an attachment of unknown content-type, it uses:

Content-Type: application/octet-stream; name=filename.kitten
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename=filename.kitten

Using the name= parameter is no longer necessary, so the following can be sent instead:

Content-Type: application/octet-stream
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename=filename.kitten

Claws already behaves this way when it sends an attachment with a known content-type, so consistency should be preferred.

Additionally, removing this name= parameter presents some message size savings.