[bug 921107] Update email in exact target

When someone changes their email in Mozillians.org, move their exact
target subscriptions to the new email address.

Also take advantage of new basket subscribe(sync=Y) to simplify
the update tasks.
[fix bug 921107] Update email in Exact Target.
Merge pull request #872 from glogiotatidis/921107

[Fix bug 921107] Update email in exact target