[Nmh-workers] Requested send feature: Silently remove blank Nmh-Attachment headers

[norm]

It would be nice, if send would silently remove blank Nmh-Attachment headers.

Then users could put them in their templates. At composition time, they could
leave them blank, fill them in, or duplicate them for multiple attachments.

That way, folks like me, wouldn't have to remember how to spell 
"Nmh-Attachment:"

Presently, when send encounters a blank Nmh-Attachment header it complains:

     send: unable to access file ""

and errors out.

    Norman Shapiro