Add test to demonstrate fatal error when accessing permitted users that are cached using the acl_cache.

This has arisen during investigation of a possible regression - it turns out that if you give the 'everyone' group
access to a contact using ACLs (or hooks I believe) they get a fatal error on any attempt at event or other registration.

The issue is that when attempting to check for duplicates the call is made using check_permission. This in itself is a possible
regression as the CRM_Dedupe_Finder::dupesByParams function now drops the check_permission key when it is equal to 0 from

https://github.com/civicrm/civicrm-core/commit/4f33e78b901fb7cdb38a3026f88b59a2f9fd2c68

So we have an issue that
1) we are now applying check_permission when doing a dupe_check from front end forms - this probably is resulting in 5.9
sites getting too many duplicates are they would always be null for anon users
2) if we DO do a permissions check when an acl or hook has been used to give anon users permission to access
contacts then they will get a fatal error. This is because it sets contact_id to 0 and attempts to insert it into the
acl_contact_cache.

I think we need to either remove the array_filter line that we think we may not need per code comments
or add specific handling for the check_permission flag

AND drop the foreign key constraint on the civicm_acl_contact_cache table. This means they will
no longer be removed when a contact is deleted but this is a clean up issue rather than one with
functionaly implications & we *should* have some form of cleanup in play on that table. In addition,
removing the constraint will reduce write contention