[FIXES JENKINS-2494] Restore correct behaviour

- Fixes a regression in core where the display name clear on copy was triggering a save
- More than one way to do this, could also have used the marker interface approach
  This route seems slightly less fragile, though people could still add ItemListeners
  with order == -Double.MAX_VALUE which would then introduce intdeterminism.
  A marker interface would remove that indeterminism as the onCopyComplete method would
  be only called on the Job as the last method... but it could be hard to
  ensure that all ItemGroupMixin's respect the calling of onCopyComplete contract
  hence this approach seems better to me for that reason

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

@@ -125,6 +125,13 @@ public abstract class Job<JobT extends Job<JobT, RunT>, RunT extends Run<JobT, R
      */
     private transient volatile boolean holdOffBuildUntilSave;
 
+    /**
+     * {@link ItemListener}s can, and do, modify the job with a corresponding save which will clear
+     * {@link #holdOffBuildUntilSave} prematurely. The {@link LastItemListener} is responsible for
+     * clearing this flag as the last item listener.
+     */
+    private transient volatile boolean holdOffBuildUntilUserSave;
+
     private volatile BuildDiscarder logRotator;
 
     /**
@@ -150,7 +157,7 @@ protected Job(ItemGroup parent, String name) {
     @Override
     public synchronized void save() throws IOException {
         super.save();
-        holdOffBuildUntilSave = false;
+        holdOffBuildUntilSave = holdOffBuildUntilUserSave;
     }
 
     @Override
@@ -204,7 +211,25 @@ public void onCopiedFrom(Item src) {
         super.onCopiedFrom(src);
         synchronized (this) {
             this.nextBuildNumber = 1; // reset the next build number
-            this.holdOffBuildUntilSave = true;
+            this.holdOffBuildUntilUserSave = true;
+            this.holdOffBuildUntilSave = this.holdOffBuildUntilUserSave;
+        }
+    }
+
+    @Extension(ordinal = -Double.MAX_VALUE)
+    public static class LastItemListener extends ItemListener {
+
+        @Override
+        public void onCopied(Item src, Item item) {
+            // If any of the other ItemListeners modify the job, they effect
+            // a save, which will clear the holdOffBuildUntilUserSave and
+            // causing a regression of JENKINS-2494
+            if (item instanceof Job) {
+                Job job = (Job) item;
+                synchronized (job) {
+                    job.holdOffBuildUntilUserSave = false;
+                }
+            }
         }
     }
 
@@ -226,7 +251,7 @@ protected void performDelete() throws IOException, InterruptedException {
         return new TextFile(new File(this.getRootDir(), "nextBuildNumber"));
     }
 
-    protected boolean isHoldOffBuildUntilSave() {
+    protected synchronized boolean isHoldOffBuildUntilSave() {
         return holdOffBuildUntilSave;
     }