When we initially created review groups, we made the assumption that all groups

would have an associated mailing list. This made a lot of sense when

transitioning from an email based code review system. Shortly after, we made

it so that any review group that didn't have a mailing list would instead send

email directly to all the members. This creates a confusing situation whereby

users are expected to subscribe to mailing lists if they're present but

otherwise get emails.
This change adds an option to review groups to specify whether emails should go

only to the list, or to the list plus every subscriber. The default for this is

to keep the current behavior.

Tested evolution.
Verified that with this check-box off, the recipient list for a review

  request assigned to a group with a mailing list contained both the mailing

  list and the group members.