Updated both the Athena and the AthenaP1 builds to pick up the latest version

of the atlasexternals repository. To fix the ZSH issues that showed up in the
Athena build, and to bring the AthenaP1 build up to date.

Since the new tag introduces a different behaviour for the package filter file,
I had to tweak the AthenaP1 filter file a bit. (The Athena file was already
updated to work correctly with the new behaviour.)