add X509_up_ref() documentation

Reviewed-by: NKurt Roeckx <kurt@openssl.org>

doc/crypto/X509_new.pod

@@ -2,7 +2,7 @@
 
 =head1 NAME
 
-X509_new, X509_free - X509 certificate ASN1 allocation functions
+X509_new, X509_free, X509_up_ref - X509 certificate ASN1 allocation functions
 
 =head1 SYNOPSIS
 
@@ -10,16 +10,26 @@ X509_new, X509_free - X509 certificate ASN1 allocation functions
 
  X509 *X509_new(void);
  void X509_free(X509 *a);
+ void X509_up_ref(X509 *a);
 
 =head1 DESCRIPTION
 
 The X509 ASN1 allocation routines, allocate and free an
 X509 structure, which represents an X509 certificate.
 
-X509_new() allocates and initializes a X509 structure.
+X509_new() allocates and initializes a X509 structure with reference count
+B<1>.
 
-X509_free() frees up the B<X509> structure B<a>.
-If B<a> is NULL nothing is done.
+X509_free() decrements the reference count of B<X509> structure B<a> and
+frees it up if the reference count is zero. If B<a> is NULL nothing is done.
+
+X509_up_ref() increments the reference count of B<a>.
+
+=head1 NOTES
+
+The function X509_up_ref() if useful if a certificate structure is being
+used by several different operations each of which will free it up after
+use: this avoids the need to duplicate the entire certificate structure.
 
 =head1 RETURN VALUES
 
@@ -27,7 +37,7 @@ If the allocation fails, X509_new() returns B<NULL> and sets an error
 code that can be obtained by L<ERR_get_error(3)>.
 Otherwise it returns a pointer to the newly allocated structure.
 
-X509_free() returns no value.
+X509_free() and X509_up_ref() do not return a value.
 
 =head1 SEE ALSO