The recently added SeatDialogText type was just what I needed to add a
method to the ssh_key vtable for dumping certificate information in a
human-readable format. It will be good for displaying in a Windows
dialog box as well as in cmdgen's text format.
This commit introduces and implements the new method, and adds a
--cert-info mode to command-line Unix PuTTYgen that uses it. The
Windows side will follow shortly.
6737a19072