Bug 273489 [Mac] We should not nest sheets
bundles/org.eclipse.ui.ide/src/org/eclipse/ui/internal/ide/dialogs/PathVariableDialog.java
* Configures this dialog's shell, setting the shell's text.
     * 
     * @see org.eclipse.jface.window.Window#configureShell(Shell)
     */
    protected void configureShell(Shell shell) {
        super.configureShell(shell);
        if (newVariable) {
			shell.setText(IDEWorkbenchMessages.PathVariableDialog_shellTitle_newVariable);
		} else {
			shell
                    .setText(IDEWorkbenchMessages.PathVariableDialog_shellTitle_existingVariable);
		}
    }
    /**
     * Creates and returns the contents of this dialog (except for the button bar).
     * 
     * @see org.eclipse.jface.dialogs.TitleAreaDialog#createDialogArea
     */
    protected Control createDialogArea(Composite parent) {
        
        Composite parentComposite = (Composite) super.createDialogArea(parent);
        initializeDialogUnits(parentComposite);
        
        
        Composite contents = createComposite(parentComposite);
         
        createWidgets(contents);
        
        if (type == EXISTING_VARIABLE) {
            nameEntered = locationEntered = true;