Bug 29853 [Workbench] OpenWithMenu and setFile
The constructor that only takes the IWorkbenchPage mentions that the user must use the setFile method...this method does not exist.
bundles/org.eclipse.ui.ide/extensions/org/eclipse/ui/actions/OpenWithMenu.java
* @param menu the menu to add the item to
     * @param file the file being edited
     */
    private void createDefaultMenuItem(Menu menu, final IFile file) {
        final MenuItem menuItem = new MenuItem(menu, SWT.RADIO);
        menuItem.setSelection(IDE.getDefaultEditor(file) == null);
        menuItem.setText(IDEWorkbenchMessages.DefaultEditorDescription_name);
        Listener listener = new Listener() {
            public void handleEvent(Event event) {
                switch (event.type) {
                case SWT.Selection:
                    if (menuItem.getSelection()) {
                        IDE.setDefaultEditor(file, null);
                        try {
                        	IEditorDescriptor desc = IDE.getEditorDescriptor(file);
                            page.openEditor(new FileEditorInput(file), desc.getId(), true, MATCH_BOTH);
                        } catch (PartInitException e) {
                            DialogUtil.openError(page.getWorkbenchWindow()
                                    .getShell(), IDEWorkbenchMessages.OpenWithMenu_dialogTitle,
                                    e.getMessage(), e);
                        }
                    }
                    break;
                }
            }
        };
        menuItem.addListener(SWT.Selection, listener);
    }
}