(doc) Limitation with autorequire of users

This notes that using SIDs will limit to finding User[SID]
and User[FQDN\Username] and won't be able to find
User[Username] (even though it is more commonly seen).

The short story is to avoid using SIDs if you need autorequire.
autorequire users

This commit provides autorequire for users that are specified in both the owner
and each of the identities in the permissions.  This will check the identity
based on the name and provider.get_account_name() to cover the cases where one
might use  SIDs versus names.