off default sort in datatables when all columns have sortable set to false

This line should probably change to:
```js
if (self.aoColumns[i].bSortable)
```
or possibly (but probably not)
```js
if (self.aoColumns[i].bSortable === true)
```
Don't use `==` for comparisons in JavaScript (source: [JavaScript, The Good Parts](http://www.amazon.com/JavaScript-Good-Parts-Douglas-Crockford/dp/0596517742))