Remove special handling of '\v'.

Remove special handling of '\v'.

I don't really like this, and it is confusing.
It exists to handle a special case of parts in a multi-part not ending
with an eol.  It is too general for that special case.  If I need
something, it should be in doc-multipart, somehow inserting a '\n' as needed.

Signed-off-by: NeilBrown <neil@brown.name>