Scheduled reminders for activities with "Choose Recipient" fails to send

(Docs may be required if we change UI.)
(Assigning to Coleman for triage.)

Steps to reproduce:

1. Checkout https://github.com/civicrm/civicrm-core/pull/7683 ( aka https://github.com/totten/civicrm-core/tree/master-16514-tests/ )
2. Run "./scripts/phpunit --group ActionSchedule CRM_AllTests"
3. Observe: CRM_Activity_ActionMappingTest fails in scenario "addAliceMeeting scheduleForAny startOnTime useHelloFirstName recipientIsBob". No messages are delivered.

That's a bit terse; in English, that's like:

1. Create contacts Alice and Bob.
2. Add an activity record (type==Meeting) for Alice (with date on Feb 1).
3. Create a scheduled reminder to deliver on the activity date.
4. Set the scheduled reminder to send an email ("Hello, <first name>").
5. Set the recipient to Bob
6. Manipulate the clock and perform several cron-runs (once a day from Jan 20 to Mar 1).

Notes:

1. For more discussion of the test, see the docblocks in https://github.com/totten/civicrm-core/blob/master-16514-tests/tests/phpunit/Civi/ActionSchedule/AbstractMappingTest.php
2. When saving an activity-based reminder in UI with "Recipients: Choose recipients", it sets "limit_to=1, recipient,=NULL, recipient_listing=NULL, recipient_manual=(CID#)". The test is engineered to match the UI. But this may not be the right behavior.

It's unclear to me whether the problem is:

• The UI and design are mismatched. (Setting an explicit recipient is not the same as limiting the recipient pool.)
• The UI saves the wrong values. (In which case we need to patch UI, patch test, make sure it works, and cleanup data during upgrade. Take care that LimitTo/AlsoInclude has another bug in CRM-17895.)

(This issue is an offshoot from CRM-16514.)