Change log to error if a plugin couldn't be loaded due to a dependency problem

Author: jameskleeh

grails-core/src/main/groovy/grails/plugins/DefaultGrailsPluginManager.java

@@ -478,7 +478,7 @@ private void loadDelayedPlugins() {
                 }
                 else {
                     failedPlugins.put(plugin.getName(), plugin);
-                    LOG.warn("WARNING: Plugin [" + plugin.getName() + "] cannot be loaded because its dependencies [" +
+                    LOG.error("ERROR: Plugin [" + plugin.getName() + "] cannot be loaded because its dependencies [" +
                             DefaultGroovyMethods.inspect(plugin.getDependencyNames()) + "] cannot be resolved");
                 }
             }