Correcting an issue where dbg_output was not defined when the server was

unreachable due to an optimization in PR#56.  Since message-id is more
useful to better pin point the correct message, removing dbg_output.

Also fixing https://github.com/OfflineIMAP/offlineimap3/issues/62 by
correcting broken multipart boundaries or raising an error if as_bytes()
fails.  Related python bug submitted: https://bugs.python.org/issue43818
although this workaround should be sufficent in the interim.

Signed-off-by: Joseph Ishac <jishac@nasa.gov>

offlineimap/folder/Base.py

@@ -26,7 +26,6 @@ from email import policy
 from email.parser import BytesParser
 from email.generator import BytesGenerator
 from email.utils import parsedate_tz, mktime_tz
-from email.errors import NoBoundaryInMultipartDefect
 
 from offlineimap import threadutil
 from offlineimap.ui import getglobalui