Rely on tests asking the names to get refused instead - test servers
should be as dumb as possible. Edited test 914, 955 and 959 accordingly.
Closes#5639
...to the client address as this frees the RCPT strings to contain
just an email address and by passing the test number into curl as the
client address remains consistent with POP3 and IMAP tests as they are
specified in the URL.
