Bug 52064 Content assist in "New Class" Dialog shows interfaces
Content Assist is available for the superclass in M7. However it also lists interfaces. If an interface is selected, the generated class "extends" it instead of "implementing" it.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/ui/wizards/NewTypeWizardPage.java
* validates the enclosing type and returns the status of the validation. It also updates the 
	 * enclosing type model.
	 * <p>
	 * Subclasses may extend this method to perform their own validation.
	 * </p>
	 * 
	 * @return the status of the validation
	 */
	protected IStatus enclosingTypeChanged() {
		StatusInfo status= new StatusInfo();
		fCurrEnclosingType= null;
		
		IPackageFragmentRoot root= getPackageFragmentRoot();
		
		fEnclosingTypeDialogField.enableButton(root != null);
		if (root == null) {
			status.setError(""); 
			return status;
		}
		
		String enclName= getEnclosingTypeText();
		if (enclName.length() == 0) {
			status.setError(NewWizardMessages.getString("NewTypeWizardPage.error.EnclosingTypeEnterName")); 
			return status;
		}
		try {
			IType type= findType(root.getJavaProject(), enclName);
			if (type == null) {
				status.setError(NewWizardMessages.getString("NewTypeWizardPage.error.EnclosingTypeNotExists")); 
				return status;