Issue #1717: rename tp_compare to tp_reserved.  I'll change the
type of tp_compare in a separate commit, for ease of reversion
should things go wrong.
diff --git a/Modules/_gdbmmodule.c b/Modules/_gdbmmodule.c
index c6817fe..de453ac 100644
--- a/Modules/_gdbmmodule.c
+++ b/Modules/_gdbmmodule.c
@@ -390,7 +390,7 @@
     0,                                  /*tp_print*/
     0,                                  /*tp_getattr*/
     0,                                  /*tp_setattr*/
-    0,                                  /*tp_compare*/
+    0,                                  /*tp_reserved*/
     0,                                  /*tp_repr*/
     0,                                  /*tp_as_number*/
     &dbm_as_sequence,                   /*tp_as_sequence*/