Follow-on email to TT ML upon addition of issue comments.

Although the issue tracker sends email to the TT ML when a new issue is
created, I noticed it is not doing so when a comment is added to an issue
(or the issue otherwise changes, e.g., change of title, product, etc).

In point of fact, I just commented on the new Issues 224 through 237, but
no messages were sent notifying this to the TT ML. This seems to be a
problem that needs resolved with the W3T. At present, the Issue tracker
automatically picks up and records messages on the ML that include the
issue number, however, the converse doesn't seem to hold.