http: Add HTTP_FLAG_FORCE_TLS and http_get_tls_info.
* common/http.c (http_parse_uri): Factor code out to ... (parse_uri): here. Add arg FORCE_TLS. (do_parse_uri): Ditto. Implement flag. (http_get_tls_info): New. (http_register_tls_ca): Allow clearing of the list. (send_request): Use a default verification function. * common/http.h (HTTP_FLAG_FORCE_TLS): New. * common/t-http.c (main): Add several command line options.