The Nutch 2.0 trunk now requires Gora, and even though it's not available in any repository, we should still configure Ivy to depend on it so that the build will work provided you follow the Gora instructions here:
I've fixed it locally and will commit an update shortly that takes care of it. In order to compile Nutch trunk now (before we get Gora into a repo), here are the steps (copied from http://github.com/enis/gora):
$ git clone git://github.com/enis/gora.git
$ cd gora
This will install Gora into your local Ivy repo. Then from there on out, just update your Ivy resolver (or alternatively just the Nutch build post this issue being resolved) and you're good.