Update mailbox attributes on list reply

The list reply contains various flags associated with the mailbox. We
should update the mailbox object with these flags when we receive a list
reply.

Signed-off-by: Marcus Karlsson <mk@acc.umu.se>
Don't send status command if \Noselect is set

We should not send the status command for a mailbox that has the
\Noselect flag set. The server will just reply with an error. Check if
the flag is set and only send the command if it's not set.

Signed-off-by: Marcus Karlsson <mk@acc.umu.se>