Document event duplicate matching

The issues CRM-14134, CRM-14540, and CRM-14541 improve the duplicate matching for anonymous users submitting event registrations. These features need to be included in documentation.

When you configure an event for online registration, you can now select an individual duplicate matching rule for matching participants with existing contacts. The default is to use the Unsupervised rule, and the rule you select takes effect for the primary participant and any additional participants.

The Online Registration tab of the Manage Event page contains a drop-down of all individual duplicate matching rules, plus the option "- Unsupervised rule ", which is the default. The Unsupervised rule itself is also in the drop-down, with the following difference: selecting the rule means that you will use that rule no matter whether it's Unsupervised, Supervised, or General. Selecting " Unsupervised rule -" uses the Unsupervised rule, whichever rule that is at the time of registration.

The multiple registrations from the same email address feature is now labeled "Same email address?" The effect is what it says: it allows you to save multiple registrants with the same email address. However, it does NOT include the old behavior of using the Unsupervised matching rule for the primary participant and the Supervised rule for the others.

Finally, the Online Registration tab now checks for whether the included profiles have enough fields to have a chance at matching participants to existing contacts. It reviews the possible combinations of matching fields that would satisfy the matching rule in effect for the event, and it checks to see if any of those combinations is present among the fields in the included profiles. The warning "Duplicate Matching Impossible" appears if there's no way to match duplicate contacts using the rule, while the warning "Duplicate Contacts Possible" appears if enough fields are there but not all of them are required.