Image embed in post body can break board display

This patch was tested on Firefox and GNOME Epiphany browsers. This patch was not tested for other browsers (i.e. IE, Chrome). Members on a board I administrate have confirmed this works for them.

Empty space below the post body occurs when it contains embedded images:
![1-before](https://f.cloud.github.com/assets/303335/2238368/a3ae383c-9bea-11e3-870e-5a62331b4ebf.png)

After applied patch:
![1-after](https://f.cloud.github.com/assets/303335/2238371/b000dfcc-9bea-11e3-9b43-478a1cb78fed.png)

Overlapping text can occur when the side menu is displayed. It is reproducible when posts contain embedded images:
![2-before](https://f.cloud.github.com/assets/303335/2238372/bb598c02-9bea-11e3-898f-0ed688cb00a0.png)

After applied patch:
![2-after](https://f.cloud.github.com/assets/303335/2238373/c0122ea2-9bea-11e3-8753-1bbf86256c06.png)