[Merge] lp:~abompard/mailman/bug-1130696 into lp:mailman

[Aurélien Bompard]

Because the digest runner is creating a MIMEMultipart instance on line 175 of src/mailman/runners/digest.py. Should we change that instead?
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https://code.launchpad.net/~abompard/mailman/bug-1130696/+merge/243226
Your team Mailman Coders is requested to review the proposed merge of lp:~abompard/mailman/bug-1130696 into lp:mailman.