[apt] Disabling upgrade to insecure packages

[Vincent Lefevre <vincent@vinc17.org>]

Is there a way to configure apt to disable the upgrade to insecure
versions of packages?

For the moment, I can't use 'apt-get dist-upgrade' as it propose me
to upgrade to
  * libpng2-dev (1.0.12-6 Debian:testing)
  * libpng2 (1.0.12-6 Debian:testing)
  * xpdf (1.01-3 Debian:testing)
(I chose to downgrade to install security updates, but don't want
to upgrade these packages to testing as long as there isn't a fix).
I need to use 'apt-get dist-upgrade -s', then 'apt-get install'...

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Vincent Lefèvre <vincent@vinc17.org> - Web: <http://www.vinc17.org/> - 100%
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