Cope with deleted users - user accounts which are literally gone

If a user account gets shutdown, then the issue assigned to that account
is no longer assigned to them - the assignee field is blank. At this point,
gu-who now just closes the issue, as there's nothing further we can do
(we don't want to bother trying to parse the issue headline, BORING!).
Add simple heuristic to see if an org looks legit

Attempt to guard against unfriendly requests.
Apply time-out to people-repo cloning, only fetch 'master'

Again, to guard against unfriendly or inconsiderate requests!
notes