Since I want git-annex to keep building on debian stable, I need to still
support the old http-client, which required explicit calls to
closeManager, or use of withManager to get Managers to close at appropriate
times. This is not needed in the new version, and so they added a
deprecation warning. IMHO much too early, because look at the mess I had to
go through to avoid that deprecation warning while supporting both
versions..