Before and After hooks support added to Rhino

Hi,

I just added Before and After hooks support to the rhino backend.
Rhino scripts can now call two new functions, `Before` and `After`, whitch receive:

* a function
* a optional string or array of strings with tag expressions for that hook
* a optional object with `timeout` and/or `order` properties

Example:

```
Before(function() {
  // do something
}, [ "@mytag" ], { timeout : 100, order : 1 });

After(function() {
  // do something
}, [ "@mytag" ]);
```