Support PolKit
Most GNU/Linux distributions have eschewed gksu and similar tools in favor of PolKit for running GTK+ applications with escalated privileges. Since baobab need to read privileged directories in order to calculate full-disk usage, baobab need usually be run escalated. Lack of PolKit support makes it difficult to use baobab on those distributions for full-disk usage analysis.
Supporting PolKit will solve this problem and additionally enable baobab to request escalation on-demand if it encounters privileged directories and/or files.