[imp] Fix for 'Document Contains No Data' NS4.7x

[Keith]

If you're getting a  'Document Contains No Data' error
message in Netscape 4.7x when you delete mail from
your POP3 inbox, try this fix (it worked for me):

Go to the "imp" directory and open "mailbox.php" in a
text editor.

Find the following block of code in "mailbox.php":

 case DELETE_MESSAGES:
     if (!empty($indices)) {
         IMP_Message::delete($indices);

         // For POP3, redirect so that refreshing the page doesn't
         // delete more messages accidentally.
         if ($imp['base_protocol'] == 'pop3') {
             header('Location: ' . Horde::applicationUrl('mailbox.php'), true);
             exit;
         }

     }
     break;

Append a parameter to the the "mailbox.php" URL.

For example, change 'mailbox.php' to 'mailbox.php?cid=1'