make close-and-halt work on new tabs in Chrome

If you open a notebook via right-click open-in-new-tab, the close-and-halt menu
item will not work. This commit fixes the issue for Chromium and IE. It is not
possible in Firefox, as new tabs/windows which were *not* opened via a script (
window.open call ) are not allowed to be closed via window.close and will yield
a message like:

```
[11:50:59.691] Scripts may not close windows that were not opened by script. @
http://localhost:8888/static/notebook/js/menubar.js:105
```