Make "list" command suppress rejected addresses by default

The "list" command now suppresses addresses that reject incoming mail
by default. If the -a command is specified, then they are listed as
before. The administrator's "list-user" command always shows all
aliases for a user, regardless of whether or not they are delivered.

[v3, squashed from c9f544da6fba by iwj]

Signed-off-by: Matthew Vernon <matthewv@chiark.greenend.org.uk>