Fix import exception window layout (see #11797).

As I've been looking at more and more exceptions, I had to finally fix this. This PR updates the layout applied to the import exception viewer. This can be easily rebased to ``dev_4_4``, as the component code is the same there.

**Before:**
![screen shot 2013-12-11 at 16 01 20](https://f.cloud.github.com/assets/1692189/1725311/cb7acca0-627d-11e3-8a3a-7477a26730be.png)

**After:**
![screen shot 2013-12-11 at 16 02 20](https://f.cloud.github.com/assets/1692189/1725315/d6d68eea-627d-11e3-9a2a-c63321538830.png)