Bug 67168 Change Signature shows error message twice [refactoring]
200406111814 public class TestClass { void change() { } x } Try to 'Change Method Signature' on 'change()'. The error message dialog always shows up twice.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/ui/actions/ModifyParametersAction.java
* Creates a new <code>ModifyParametersAction</code>. The action requires
	 * that the selection provided by the site's selection provider is of type <code>
	 * org.eclipse.jface.viewers.IStructuredSelection</code>.
	 * 
	 * @param site the site providing context information for this action
	 */
	public ModifyParametersAction(IWorkbenchSite site) {
		super(site);
		setText(RefactoringMessages.getString("RefactoringGroup.modify_Parameters_label"));
		WorkbenchHelp.setHelp(this, IJavaHelpContextIds.MODIFY_PARAMETERS_ACTION);
	}
	
	/*
	 * @see SelectionDispatchAction#selectionChanged(IStructuredSelection)
	 */
	public void selectionChanged(IStructuredSelection selection) {
		try {
			setEnabled(canEnable(selection));
		} catch (JavaModelException e) {
			
			if (JavaModelUtil.filterNotPresentException(e))
				JavaPlugin.log(e);
			setEnabled(false);
		}
	}
    /*
     * @see SelectionDispatchAction#selectionChanged(ITextSelection)
     */
	public void selectionChanged(ITextSelection selection) {
		setEnabled(true);