Fall back to HTTP for fetching automatically

Fall back to HTTP for fetching automatically

Drop the "Unable to connect using https. Use http instead?" question as it
does not provide any security benefit;  SHA256.sig is used to verify sets.

Do provide an informative message iff the fallback happened such that
installations/upgrades that cannot Get/Verify first but Install directly
can be aborted in lack of SHA256.sig, i.e. sets were fetched over HTTP and
verification would be skipped.

Discussed with deraadt tb
OK deraadt