show medium avatar in hovercard

### before
![hovercard_before](https://f.cloud.github.com/assets/3798614/622930/8caeb1f2-cf53-11e2-8b09-d7b8c90a2adb.png)
### after
![hovercard_after](https://f.cloud.github.com/assets/3798614/622931/8f119716-cf53-11e2-9f2c-da4d4a454244.png)