AS2 Draft Update with Cyclone's new ABNF

Update to section 4 at Cyclone's request.

The draft yesterday said to quote the string if there were
contiguous embedded spaces.  This one says to quote if there
are any spaces (or DQUOTE or backslash).

This is better.

If there are no further comments, I will send this to IETF
to post tomorrow.

David Fischer
Drummond Group.