CHUNKING extension for mailfront

I have added the CHUNKING extension to mailfront.  It adds BDAT with a byte
count as an alternative to DATA with dot stuffing.  It's not hugely faster, but
it's a little faster and gmail and outlook/hotmail/live prefer it over data.

It's a modified version of protocol-smtp.c because it shares a lot of local
static routines with the data command.  If you'd like a copy, just ask.

RFC 3030 which defines CHUNKING and BDAT also defines BINARYMIME which I did not
implement because it's a lot harder.  The DATA and BDAT commands strip out
carriage returns in the received data using a simple scheme that throws them all
away unless they're doubled.  To do BINARYMIME properly it'd need to parse the
MIME structure of the message and throw away the carriage returns except inside
a block of binary MIME data.  Parsing the MIME structure of the message after
you've received it is hard enough, parsing on the fly is hopeless.  It's also a
lot less widely supported. Hotmail does, but Gmail doesn't.

Regards,
John Levine, [email protected], Primary Perpetrator of "The Internet for Dummies",
Please consider the environment before reading this e-mail. https://jl.ly