* adjust learning of ham
See #3333
When moving a mail from the Junk folder to the Trash folder, the mail
previously classified as ham due to the wildcard match of `*`. Because
the syntax does not allow for negation, we can only change the behavior
in a way that mails are learned as ham when they are moved into `INBOX`
from `Junk`. This is reasonable though.
* adjust tests accordingly
* adjust docs accordingly