This both is better copy and also cleared for translators, who in
languages with gendered nouns don't need to guess what gender to use
for "one" without context.
This completes the last commit's work to fix CVE-2017-0910, applying
to any invite links already created before the fix was deployed. With
this change, all new-user registrations must match an explicit realm
in the PreregistrationUser row, except when creating a new realm.
[greg: rewrote commit message]
Tim Abbott
Vishnu KS
Utkarsh Patil
Vishnu Ks