Document X509_get_serialNumber and X509_set_serialNumber.

Reviewed-by: NRich Salz <rsalz@openssl.org>
Reviewed-by: NViktor Dukhovni <viktor@openssl.org>

doc/crypto/X509_get_serialNumber.pod

+=pod
+
+=head1 NAME
+
+X509_get_serialNumber, X509_set_serialNumber - get or set certificate serial
+number.
+
+=head1 SYNOPSIS
+
+ #include <openssl/x509.h>
+
+ ASN1_INTEGER *X509_get_serialNumber(X509 *x);
+ int X509_set_serialNumber(X509 *x, ASN1_INTEGER *serial);
+
+=head1 DESCRIPTION
+
+X509_get_serialNumber() returns the serial number of certificate B<x> as an
+B<ASN1_INTEGER> structure which can be examined or initialised. The value
+returned is an internal pointer which B<MUST NOT> be freed up after the call.
+
+X509_set_serialNumber() sets the serial number of certificate B<x> to
+B<serial>. A copy of the serial number is used internally so B<serial> should
+be freed up after use.
+
+=head1 RETURN VALUES
+
+X509_get_serialNumber() returns an B<ASN1_INTEGER> structure.
+
+X509_set_serialNumber() returns 1 for success and 0 for failure.
+
+=head1 SEE ALSO
+
+L<d2i_X509(3)>,
+L<ERR_get_error(3)>,
+L<X509_CRL_get0_by_serial(3)>,
+L<X509_get0_signature(3)>,
+L<X509_get_ext_d2i(3)>,
+L<X509_get_extension_flags(3)>,
+L<X509_get_pubkey(3)>,
+L<X509_get_subject_name(3)>,
+L<X509_NAME_add_entry_by_txt(3)>,
+L<X509_NAME_ENTRY_get_object(3)>,
+L<X509_NAME_get_index_by_NID(3)>,
+L<X509_NAME_print_ex(3)>,
+L<X509_new(3)>,
+L<X509_sign(3)>,
+L<X509V3_get_d2i(3)>,
+L<X509_verify_cert(3)>
+
+=head1 HISTORY
+
+X509_get_serialNumber() and X509_set_serialNumber() are available in
+all versions of OpenSSL.
+
+=cut