Latest changes:

 - Move the CertItem class from ValidateCertificateResponse class to
    CertValidateMessage class

  - Add the Ssl::CertValidateMessage::getCertByName method to search
    an for a certificate in a std::vector<CertItem> list

  - Implement the Ssl::ValidateCertificateResponse::getError to search in
    Ssl::ValidateCertificateResponse::errors list for a error

  - Improve the Ssl::CertValidateMessage::parseResponse method

  - Remove the ValidateCertificateResponse::ErrorItem::certId member. The
    user should always link with a certificate, not with an index to certificate.

  - The CertValidateMessage::parseResponse takes as argument the list of peer
    Certificates. It uses this list to fill the ValidateCertificateResponse
    object.

  - Return ERR_GATEWAY_FAILURE/HTTP_INTERNAL_SERVER_ERROR error if:
     * Failed to compose the  Ssl::CertValidateMessage message to sent to
       cert validator
     * The response from cert validator is wrong
     * The cert validator returns an error.

  - Implement the FwdState::sslCrtvdCheckForErrors method. This method
    checks if the errors returned from cert validator class can be
    ignored or an error to the user must returned.

  - Now if the Config.ssl_client.cert_error is not used, then the first
    error in the list returned from cert validator, is the error which
    considered as the error which causes the failure