problems: controls are now destroyed and recreated on a panel
switch. In addition, this patch also introduces a better means of
doing the group boxes.
[originally from svn r884]
features (prompt for passphrase twice, prompt before overwriting a
file, check the key file was actually saved OK), testing of the
generated keys to make sure I got the file format right, and support
for a variable key size. I think what's already here is basically
sound though.
[originally from svn r715]
