httputil: nicer UI message when lacking ssl

httputil: nicer UI message when lacking ssl

Rather than complaining about a missing use_ssl= method, if net/https
fails to load we define a mock use_ssl= method that raises a runtime
error making the LoadError message public. This is not the most
user-friendly message (we would prefer not to expose internals), but
it should be clear enough to help owners that forget to read the log
find what's missing.