Enabled concurrent build support for matrix projects

core/src/main/java/hudson/matrix/MatrixConfiguration.java

@@ -78,6 +78,16 @@ public class MatrixConfiguration extends Project<MatrixConfiguration,MatrixRun>
         super.onLoad(parent, combination.toString());
     }
 
+    @Override
+    public boolean isConcurrentBuild() {
+        return getParent().isConcurrentBuild();
+    }
+
+    @Override
+    public void setConcurrentBuild(boolean b) throws IOException {
+        throw new UnsupportedOperationException("The setting can be only changed at MatrixProject");
+    }
+
     /**
      * Used during loading to set the combination back.
      */

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

@@ -299,7 +299,7 @@ public abstract class AbstractProject<P extends AbstractProject<P,R>,R extends A
      */
     @Exported
     public boolean isConcurrentBuild() {
-        return Jenkins.CONCURRENT_BUILD && concurrentBuild;
+        return concurrentBuild;
     }
 
     public void setConcurrentBuild(boolean b) throws IOException {

core/src/main/java/jenkins/model/Jenkins.java

@@ -213,6 +213,8 @@ import org.jvnet.hudson.reactor.TaskBuilder;
 import org.jvnet.hudson.reactor.TaskGraphBuilder;
 import org.jvnet.hudson.reactor.Reactor;
 import org.jvnet.hudson.reactor.TaskGraphBuilder.Handle;
+import org.kohsuke.accmod.Restricted;
+import org.kohsuke.accmod.restrictions.NoExternalUse;
 import org.kohsuke.args4j.Argument;
 import org.kohsuke.args4j.Option;
 import org.kohsuke.stapler.Ancestor;
@@ -3802,7 +3804,10 @@ public class Jenkins extends AbstractCIBase implements ModifiableItemGroup<TopLe
      * When we merge this back to the trunk, this allows us to keep
      * this feature hidden for a while until we iron out the kinks.
      * @see AbstractProject#isConcurrentBuild()
+     * @deprecated as of 1.464
+     *      This flag will have no effect.
      */
+    @Restricted(NoExternalUse.class)
     public static boolean CONCURRENT_BUILD = true;
 
     /**