Add nameConstraints commonName checking.

Add nameConstraints commonName checking.

New hostname checking function asn1_valid_host()

Check commonName entries against nameConstraints: any CN components in
EE certificate which look like hostnames are checked against
nameConstraints.

Note that RFC5280 et al only require checking subject alt name against
DNS name constraints.

Reviewed-by: Richard Levitte <levitte@openssl.org>