Fix scroll bars shown in Revert dialogue box


## What does this MR do?

Eliminate scroll bars shown in Revert dialogue box, see the screenshots.

## Are there points in the code the reviewer needs to double check?

N/A

## Why was this MR needed?

Ugly scroll bars are shown in Revert dialogue box.

## What are the relevant issue numbers?

N/A

## Screenshots

![Screen_Shot_2016-04-05_at_15.27.10](/uploads/428295858ada7cd2fcdf1e831c42f8ec/Screen_Shot_2016-04-05_at_15.27.10.png)



See merge request !3532