Adding a check to make sure the check all box exists before checking to ...

...see if it has been checked.

There is an javascript error currently error when the select all check box does not show for pages larger than the maximum batch size.
![screen shot 2014-08-01 at 3 32 17 pm](https://cloud.githubusercontent.com/assets/1599081/3783955/a376a052-19b2-11e4-9ddc-e8bd121194a6.png)