Added a clear to render product #poststuff height

I have added a clear so that the #poststuff's height is properly
rendered, not having this can affect a lot of javascript manipulations.
Category #poststuff height similar to #2348

https://github.com/ingenesis/shopp/issues/2348

I have added a clear so that the #poststuff's height is properly
rendered, not having this can affect a lot of javascript manipulations.
Merge pull request #2348 from WazzaJB/master

Added a clear to render #poststuff height