This is good, but I think it would be great if the error message helped the end user with next steps to make this work.  For example, perhaps a URL to a document that describes how to enable the augeas feature in Puppet.

Hopefully we have this documented at http://docs.puppetlabs.com/

Maybe something like, "requires the ruby augeas bindings. Information about how to satisfy this requirements is available at: http://..."

I think this would be great because a ParseError aborts catalog compilation entirely, so the user is sort of "stuck" if they encounter this error.