[MNG-3400] Implement clone properly following Effective Java' book considerations

git-svn-id: https://svn.apache.org/repos/asf/maven/components/trunk@627935 13f79535-47bb-0310-9956-ffa450edef68

maven-core/src/main/java/org/apache/maven/lifecycle/statemgmt/StartForkedExecutionMojo.java

@@ -28,9 +28,17 @@ public class StartForkedExecutionMojo
         getLog().info( "Starting forked execution [fork id: " + forkId + "]" );
 
         if ( project != null )
+        {
+            try
             {
                 session.addForkedProject( (MavenProject) project.clone() );
             }
+            catch ( CloneNotSupportedException e )
+            {
+                throw new IllegalStateException( "MavenProject instance of class " + project.getClass().getName() +
+                    " does not support clone " );
+            }
+        }
     }
 
 }