Unsubscribe does not add a changelog timestamp

When a user clicks a link in CiviMail to unsubscribe to all lists on the service, the "No bulk Emails" flag is added to her record.

However, no corresponding entry is added to the Change Log for that record.

Seeing when someone unsubscribed from an organization's mailings is critical in many situations – for example, merging two records, one of which has the flag set and the other of which doesn't. Or to determine if a particular happening was followed by a bunch of unsubscriptions.

Obviously the Change Log provides only very limited information, but it is still often helpful – of all possible changes, I would definitely expect unsubscription to be logged.