Undocumented feature: MHMailbox sets the msg object's _mh_msgno attribute to the (stringized) message number (if this attribute is settable).  This is useful so users of this class can report the correct message number (e.g. when classifying spam).
Undocumented feature: MHMailbox sets the msg object's _mh_msgno
attribute to the (stringized) message number (if this attribute is
settable).  This is useful so users of this class can report the
correct message number (e.g. when classifying spam).

Also added a blank line before the first method of each class.

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator