added another convenience method

git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@13023 71c3de6d-444a-0410-be80-ed276b4c234a

core/src/main/java/hudson/model/Executor.java

@@ -149,6 +149,13 @@ public class Executor extends Thread implements ModelObject {
         return executable==null;
     }
 
+    /**
+     * The opposite of {@link #isIdle()} — the executor is doing some work.
+     */
+    public boolean isBusy() {
+        return executable!=null;
+    }
+
     /**
      * If this thread dies unexpectedly, obtain the cause of the failure.
      *