FIX: UploadField height calculation fix (fixes #2862 & #2863)

Minor tweaks to the calculated height. Needs IE9 testing if anyone feels like doing that for me :).

Before:
<img src="https://f.cloud.github.com/assets/1655548/2201546/93bfb5f6-98f0-11e3-9385-1ae43b15d9b7.png" width="520" height="612" />

After:
<img src="https://f.cloud.github.com/assets/1655548/2201549/99fee612-98f0-11e3-98e5-19b17af39419.png" width="526" height="589" />

IE8 before:
![screen shot 2014-02-19 at 17 08 53](https://f.cloud.github.com/assets/1655548/2209179/9fd13cd2-9988-11e3-8a00-0e60e83e1e80.png)

IE8 after:
![screen shot 2014-02-19 at 17 07 51](https://f.cloud.github.com/assets/1655548/2209183/a5d1a5d6-9988-11e3-8637-df31e36b1fbb.png)