fixup! EVP: Add EVP_PKEY_get_default_digest_name() and use it

doc/man3/EVP_PKEY_get_default_digest_nid.pod

@@ -2,31 +2,44 @@
 
 =head1 NAME
 
-EVP_PKEY_get_default_digest_nid - get default signature digest
+EVP_PKEY_get_default_digest_nid, EVP_PKEY_get_default_digest_name
+- get default signature digest
 
 =head1 SYNOPSIS
 
  #include <openssl/evp.h>
+
+ int EVP_PKEY_get_default_digest_name(EVP_PKEY *pkey,
+                                      char *mdname, size_t mdname_sz)
  int EVP_PKEY_get_default_digest_nid(EVP_PKEY *pkey, int *pnid);
 
 =head1 DESCRIPTION
 
-The EVP_PKEY_get_default_digest_nid() function sets B<pnid> to the default
-message digest NID for the public key signature operations associated with key
-B<pkey>. Note that some signature algorithms (i.e. Ed25519 and Ed448) do not use
-a digest during signing. In this case B<pnid> will be set to NID_undef.
+EVP_PKEY_get_default_digest_name() fills in the default message digest
+name for the public key signature operations associated with key
+I<pkey> into I<mdname>, up to at most I<mdname_sz> bytes including the
+ending NUL byte.
+
+EVP_PKEY_get_default_digest_nid() sets I<pnid> to the default message
+digest NID for the public key signature operations associated with key
+I<pkey>.  Note that some signature algorithms (i.e. Ed25519 and Ed448)
+do not use a digest during signing.  In this case I<pnid> will be set
+to NID_undef.  This function is only reliable for legacy keys, which
+is keys loaded from engines, or created with internal libcrypto
+implementations (B<EVP_PKEY_ASN1_METHOD>).
 
 =head1 NOTES
 
 For all current standard OpenSSL public key algorithms SHA256 is returned.
 
 =head1 RETURN VALUES
 
-The EVP_PKEY_get_default_digest_nid() function returns 1 if the message digest
-is advisory (that is other digests can be used) and 2 if it is mandatory (other
-digests can not be used).  It returns 0 or a negative value for failure. In
-particular a return value of -2 indicates the operation is not supported by the
-public key algorithm.
+EVP_PKEY_get_default_digest_name() and EVP_PKEY_get_default_digest_nid()
+both return 1 if the message digest is advisory (that is other digests
+can be used) and 2 if it is mandatory (other digests can not be used).
+They return 0 or a negative value for failure.  In particular a return
+value of -2 indicates the operation is not supported by the public key
+algorithm.
 
 =head1 SEE ALSO