Document return value of X509_add_ext

and also X509_delete_ext()
Reviewed-by: NMatt Caswell <matt@openssl.org>

doc/man3/X509v3_get_ext_by_NID.pod

@@ -115,8 +115,8 @@ initial extension will not be checked.
 
 X509v3_get_ext_count() returns the extension count.
 
-X509v3_get_ext() and X509v3_delete_ext() return an B<X509_EXTENSION> pointer
-or B<NULL> if an error occurs.
+X509v3_get_ext(), X509v3_delete_ext() and X509_delete_ext() return an
+B<X509_EXTENSION> pointer or B<NULL> if an error occurs.
 
 X509v3_get_ext_by_NID() X509v3_get_ext_by_OBJ() and
 X509v3_get_ext_by_critical() return the an extension index or B<-1> if an
@@ -124,6 +124,8 @@ error occurs.
 
 X509v3_add_ext() returns a stack of extensions or B<NULL> on error.
 
+X509_add_ext() returns 1 on success and 0 on error.
+
 =head1 SEE ALSO
 
 L<X509V3_get_d2i(3)>