This patch fixes various aspects of the attachment-saving

This patch fixes various aspects of the attachment-saving
user interface.  Changes include:

* When tagging and saving multiple attachments, you can now use the
  same target directory for multiple attachments.

* When you can't save an attachment, you get an opportunity to enter
  a new file name.

* The menu cursor will highlight the attachment that you are
  currently discussing with mutt.

* Various bug fixes.

This does, in particular, address #1619 (Debian#208430).