this is pretty slow if you have thousands of repos, since it has to read
and parse a 'gl-conf' file for every repo. (For example, on a Lenovo
X201 thinkpad with 11170 repos and a cold cache, it took 288 seconds).
(With a hot cache -- like if you run the command again -- it took 2.1
seconds! So if you have a fast disk this may not be an issue for you
even if you have 10,000+ repos).
