Mailbox list may not be properly displayed in a standard 80-column
terminal window if the $folder variable contains a long URL.  In such
a case only left part of each entry name can be visible with the default
value of $folder_format.  What's worse, this visible part may not be
enough to distinguish between the entries.

Thus in this case mutt_pretty_mailbox() will be just as useful as for
local mailboxes.