Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/15949)
=head1 NOTES
+The PEM reading functions will skip any extraneous content or PEM data of
+a different type than they expect. This allows for example having a certificate
+(or multiple certificates) and a key in the PEM format in a single file.
+
The old B<PrivateKey> write routines are retained for compatibility.
New applications should write private keys using the
PEM_write_bio_PKCS8PrivateKey() or PEM_write_PKCS8PrivateKey() routines