how to revert dependents to pre 'upgrade outdated' versions

[Ryan Schmidt]

On Jan 18, 2011, at 14:14, Bradley Giesbrecht wrote:

> Thumbnail "png" generation using ImageMagick is broken for me. I think it's due to libpng. I have activated the prior version of libpng.
> 
> How can I revert all the software that was upgraded in the last "port upgrade outdated" command to the last version before the update?

http://trac.macports.org/wiki/howto/InstallingOlderPort

As far as I know, there is no automated way to identify all such ports that were upgraded because of png.