*Don’t merge* FIX: UploadField height calculation fix (fixes #2862 & #2863)

Minor tweaks to the calculated height, to be tested in IE 8, 9 & 10.

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" />