impl TestNGContainerWizardPage so that users can add "TestNG Library"

via
"Build Path -> Add Libraries... -> TestNG"

plugin.xml

@@ -373,5 +373,13 @@
 
     </menuContribution>
   </extension>
+ <extension
+       point="org.eclipse.jdt.ui.classpathContainerPage">
+    <classpathContainerPage
+          class="org.testng.eclipse.ui.buildpath.TestNGContainerWizardPage"
+          id="org.testng.TESTNG_CONTAINER"
+          name="TestNG">
+    </classpathContainerPage>
+ </extension>
 
 </plugin>

src/main/org/testng/eclipse/TestNGMessages.properties

@@ -125,3 +125,6 @@ NewTestNGClassWizard.alreadyExists.message=File {0} already exists. Overwrite it
 
 TestNGMethodWizardPage.description=Select which methods you'd like to test.
 
+TestNGContainerWizardPage.title=TestNG Library
+TestNGContainerWizardPage.description=Set the TestNG Library for this project.
+TestNGContainerWizardPage.message=This will set the default TestNG Library to this project.

src/main/org/testng/eclipse/ui/buildpath/TestNGContainerWizardPage.java

@@ -0,0 +1,49 @@
+package org.testng.eclipse.ui.buildpath;
+
+import org.eclipse.jdt.core.IClasspathEntry;
+import org.eclipse.jdt.core.JavaCore;
+import org.eclipse.jdt.ui.wizards.IClasspathContainerPage;
+import org.eclipse.jface.dialogs.Dialog;
+import org.eclipse.jface.wizard.WizardPage;
+import org.eclipse.swt.SWT;
+import org.eclipse.swt.layout.GridLayout;
+import org.eclipse.swt.widgets.Composite;
+import org.eclipse.swt.widgets.Label;
+import org.testng.eclipse.TestNGPlugin;
+import org.testng.eclipse.buildpath.TestNGContainerInitializer;
+import org.testng.eclipse.util.ResourceUtil;
+
+public class TestNGContainerWizardPage extends WizardPage implements IClasspathContainerPage {
+
+  public TestNGContainerWizardPage() {
+    super("TestNGContainerWizardPage"); //$NON-NLS-1$
+    setTitle(ResourceUtil.getString("TestNGContainerWizardPage.title"));  //$NON-NLS-1$
+    setDescription(ResourceUtil.getString("TestNGContainerWizardPage.description")); //$NON-NLS-1$
+    setImageDescriptor(TestNGPlugin.getImageDescriptor("wizban/addlibrary_wiz.png")); //$NON-NLS-1$
+  }
+
+  public void createControl(Composite parent) {
+    Composite container = new Composite(parent, SWT.NONE);
+    GridLayout layout = new GridLayout();
+    layout.marginHeight = 0;
+    layout.marginWidth = 0;
+    container.setLayout(layout);
+
+    new Label(container, SWT.NONE).setText(ResourceUtil.getString("TestNGContainerWizardPage.message")); //$NON-NLS-1$
+
+    setControl(container);
+    Dialog.applyDialogFont(container);
+  }
+
+  public boolean finish() {
+    return true;
+  }
+
+  public IClasspathEntry getSelection() {
+    return JavaCore.newContainerEntry(TestNGContainerInitializer.TESTNG_PATH);
+  }
+
+  public void setSelection(IClasspathEntry containerEntry) {
+  }
+
+}