Use the clutter embed instead of the window as size reference

Using the clutter embed as size reference is more reliable, as not all window managers support hiding the menubar. The TerminalView will otherwise always be a couple of pixels too tall.

I also had to make sure keybinder-3.0 is requested, otherwise it would fail running as it mixes Gtk+-2 and 3 elements, not sure how you got it to run. (Valac-0.18 on Ubuntu 13.04 here)