R1:3fbad684c142

More completely explain why we're refusing to send reset mail to an unverified address

Summary:
See PHI78. The user was getting this message and (reasonably) interpreted it to mean "reset mail can never be sent to unverified addresses".

Reword it to be more clear, albeit an entire paragraph long. I don't really have a good solution in these cases where we'd need a whole page to explain what's happening (this, plus "we can't tell you which address you should use because an attacker could get information…