Improve Ember.inspect

`Ember.inspect` couldn't inspect other than a direct instance of `Object`:

``` javascript
> Ember.inspect(/regexp/); //=> '{}'
```


So I fixed to support some objects to be inspected correctly.

For examples:

``` javascript
> Ember.inspect([1, 2, 3]); //=> '[1,2,3]'
> Ember.inspect(/regexp/); //=> '/regexp/'
> Ember.inspect(new Date("Sat Apr 30 2011 13:24:11")); //=> 'Sat Apr 30 2011 13:24:11 GMT+0900 (JST)'
> Ember.inspect(new Error("Oops"); //=> 'Error: Oops'
```