This allows users to edit password files using temporary files created
in /dev/shm. This commit also tidies other things up and fixes minor
bugs and griviences that should be separate commits but aren't.

Reported-by: rupa <rupa@lrrr.us>

Add a --no-echo flag to the insert operation so that the password isn't
echoed when entering it. This requires the user to echo the password
twice for confirmation.

Reported-by: Dominic Lüchinger <d.luechinger@snowgarden.ch>