Tab bar above document option

This change adds new option for showing tab bar only above document, so the
file browser header lines up with tab bar.

![TM2 with tabs above document](https://f.cloud.github.com/assets/103067/91954/39974a8a-65b6-11e2-9527-9a932ebfba5c.png)

File browser header height reduced by 1 pixel to match tab bar height. It also
draws optional top divider when in same line as tab bar.