Try: deleting ~/.m2/repository/org/codehaus and then build maven-model.
Somehow plugin dependencies are not resolved; weird that this doesn't occur more often.
This is because in DefaultPluginManager the verifyPlugin method calls checkRequiredMavenVersion
with just the PluginArtifactRepositories. The checkRequiredMavenVersion resolves the plugin and/or
its dependencies but does not have access to the normal artifact repositories, so only plugin repositories
can be searched for the plugin's dependencies.
Modified the verifyPlugin method to add the RemoteArtifactRepositories to the list.