Squad info in Dwarf Manipulator screen

This is a little thing I was craving for while using the fantastic Dwarf Manipulator screen.

![Dwarf Manipulator](https://raw.githubusercontent.com/pierredavidbelanger/dfhack/manipulator_show_squad/images/manipulator2.png)

I tested this with a couple saves and it works well.

I am testing with `df 0.34.11` on `OS X 10.9.4` 
using `cmake version 2.8.12.2` and `gcc-mp-4.5 (MacPorts gcc45 4.5.4_9+universal) 4.5.4`

This is my first contribution to dfhack, I hope I did everything correctly.
Do not hesitate to let me know if I need to change/fix something in this PR