Adding a libtiff dep?

[Richard Hughes <hughsient gmail com>]

To fix https://bugzilla.gnome.org/show_bug.cgi?id=609444, I need to
add a libtiff hard dep on gnome-color-manager. All distros should
already be installing this by default, but I wanted to check to see if
anyone had any issue with this.

Speak now, or forever hold your peace! :-)

Thanks,

Richard.