[bug-mailutils] mail -E 'set readonly=yes' still allows mailbox(dir) modification

[積丹尼 Dan Jacobson]

Mail saved when
$ mail -E 'set readonly=yes'
is used are still deleted from Maildir, despite documetation

'readonly'

     Type: Boolean
     Default: False

     When set, mailboxes are opened in readonly mode.  In this mode, any
     'mail' commands that alter the contents of the mailbox are
     disabled.  These commands include, but are not limited to:
     'delete', 'save' and 'mbox'.