Add jQuery closure for compatibility when using concurrent jQuery instances

When a page includes 2+ copies of jQuery, the common pattern is:

```
<script type="text/javascript" src="jquery-1.8.js"></script>
<script type="text/javascript" src="plugin-1.js"></script>
<script type="text/javascript" src="plugin-2.js"></script>

<script type="text/javascript">
var jQuery_1_8 = $.noConflict(true);
</script>

<script type="text/javascript" src="jquery-1.9.js"></script>
<script type="text/javascript" src="plugin-3.js"></script>
<script type="text/javascript" src="plugin-4.js"></script>
```

In this example, plugin-1 is bound to jQuery 1.8 while plugin-3 is bound to
jQuery 1.9.  This pattern only works reliably when plugin-*.js include
closures.

Without the closure, plugin-1.js is liable to skip around senselessly among
v1.8 and v1.9 (depending on the details of how it's coded).