Added CURLOPT_HTTP09_ALLOWED and --http0.9 for this purpose.
For now, both the tool and library allow HTTP/0.9 by default.
docs/DEPRECATE.md lays out the plan for when to reverse that default: 6
months after the 7.64.0 release. The options are added already now so
that applications/scripts can start using them already now.
Fixes#2873Closes#3383
Deal with tiny "HTTP/0.9" (header-less) responses by checking the
status-line early, even before a full "HTTP/" is received to allow
detecting 0.9 properly.
Test 1266 and 1267 added to verify.
Fixes#2420Closes#2872
