Revision 169379

o Cleaned up a couple of things in repoclean that broke with the last update.
o Added concept of ErrorDiagnoser to help interpret errors and provide user feedback
o Added PluginParameterException to provide richer information than simply PluginConfigurationException (it's derived from PluginConfigurationException)
o Added implementations of ErrorDiagnoser for artifact resolution and plugin configuration handling.
o Modified DefaultMaven's logFailure(..) method to use errorDiagnosers Map (injected via Plexus)

I approached the plugin parameter expression/name feedback in this way, as it seems like a general pattern for interpreting errors without embedding this logic deep within the app itself. Feel free to rollback if this causes issues.