[MlMt] don't like auto-add

[Randy Bush]

>> my issue is not that Sent/Drafts/... exist.  i just do not want to be
>> gratuitously subscribed to them in SOURCES.  the issue is screen real
>> estate.
> 
> To the right of the SOURCES label is a “Hide” button, nicely hidden
> from plain view until you mouse over it. Just in case you weren’t
> already aware of this.

i am not trying to hide the SOURCES list; it is my main index.  fwiw, i
have MAILBOXES hidden.

my issue is that i do not want to be gratuitously subscribed to new
mailboxes in SOURCES.  i maintain the list very carefully, and have
a length constraint due to screen real estate.

randy