[FIXED JENKINS-8929] Changed the definition of a building downstream project...

[FIXED JENKINS-8929] Changed the definition of a building downstream project to one that is Building, Waiting, Pending or Buildable
but NOT blocked.  This prevents the deadlock condition where upstream project A is blocked on downstream project B, which is
blocked on upstream project A - now in this scenario B will remain blocked but A will build, eventually freeing up B.

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

@@ -100,6 +100,7 @@ import java.util.Collection;
 import java.util.Collections;
 import java.util.Comparator;
 import java.util.HashSet;
+import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
@@ -1082,9 +1083,10 @@ public abstract class AbstractProject<P extends AbstractProject<P,R>,R extends A
     protected AbstractProject getBuildingDownstream() {
     	DependencyGraph graph = Hudson.getInstance().getDependencyGraph();
         Set<AbstractProject> tups = graph.getTransitiveDownstream(this);
-        tups.add(this);
+        Queue queue = Hudson.getInstance().getQueue();
+
         for (AbstractProject tup : tups) {
-            if(tup!=this && (tup.isBuilding() || tup.isInQueue()))
+			if(tup.isBuilding() || queue.getUnblockedItems().containsKey(tup))
                 return tup;
         }
         return null;

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

@@ -77,6 +77,7 @@ import java.util.Collections;
 import java.util.GregorianCalendar;
 import java.util.HashMap;
 import java.util.Iterator;
+import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
 import java.util.NoSuchElementException;
@@ -633,6 +634,17 @@ public class Queue extends ResourceController implements Saveable {
         return new ArrayList<BuildableItem>(pendings.values());
     }
 
+    /**
+     * Gets all items that are in the queue but not blocked
+     */
+    synchronized ItemList<Item> getUnblockedItems() {
+    	ItemList<Item> queuedNotBlocked = new ItemList<Item>();
+        queuedNotBlocked.addAll(waitingList);
+        queuedNotBlocked.addAll(pendings);
+        queuedNotBlocked.addAll(buildables);
+        return queuedNotBlocked;
+    }
+
     /**
      * Is the given task currently pending execution?
      */
@@ -1557,7 +1569,7 @@ public class Queue extends ResourceController implements Saveable {
     /**
      * {@link ArrayList} of {@link Item} with more convenience methods.
      */
-    private static class ItemList<T extends Item> extends ArrayList<T> {
+    static class ItemList<T extends Item> extends ArrayList<T> {
     	public T get(Task task) {
     		for (T item: this) {
     			if (item.task == task) {