url: add CURLOPT_SSL_VERIFYSTATUS option

This option can be used to enable/disable certificate status verification. The
certificate status can be obtained by using the "Certificate Status Request" TLS
extension defined in RFC6066 section 8, or by using the OCSP protocol defined in
RFC6960.
openssl: add support for the Certificate Status Request TLS extension

Also known as "status_request" or OCSP stapling. This is defined in RFC6066
section 8.
gtls: add support for the Certificate Status Request TLS extension

Also known as "status_request" or OCSP stapling. This is defined in RFC6066
section 8, and requires GnuTLS 3.1.3 or higher.