🚀 go-pugleaf

The Content-Type header is described in RFC 1049; I'm not sure
where Content-Length originated.  The SVR4 usage of Content-Type
doesn't look like anything in RFC 1049.

RFC 1154 updates RFC 1049, and describes a much more useful
encapsulation format.  I was able to read this RFC back in '90 a
bit before it was published and I was quite pleased with it.
Unfortunately it looks like 1154 is being ignored.

As far as I can tell both RFC 1049 and 1154 were meant to specify
ways of encapsulating different types of messages within an existing
RFC 822 message, _not_ to specify a folder format.  I hope SVR4
doesn't surprise us with any more unbridled bursts of creativity.

If SVR4 /bin/mail no longer quotes lines beginning with "From ",
then I'll have to make VM a bit more clever about recognizing
message separators.  Irritating, but becoming increasingly
necessary in the face of things like Deliver script that don't do
the quoting either.