Work around cpychecker false positive in conn_tpc_begin()

See davidmalcolm/gcc-python-plugin#109

Author: dvarrazzo

psycopg/connection_int.c

@@ -1352,6 +1352,17 @@ conn_set_client_encoding(connectionObject *self, const char *pgenc)
 }
 
 
+/* Set the xid in the connection status.
+ *
+ * Simple function to separate the ref stealing semantic and work around
+ * davidmalcolm/gcc-python-plugin#109
+ */
+STEALS(2) IGNORE_REFCOUNT static void
+conn_set_xid(connectionObject *self, xidObject *xid)
+{
+    self->tpc_xid = xid;
+}
+
 /* conn_tpc_begin -- begin a two-phase commit.
  *
  * The state of a connection in the middle of a TPC is exactly the same
@@ -1383,7 +1394,7 @@ conn_tpc_begin(connectionObject *self, xidObject *xid)
 
     /* The transaction started ok, let's store this xid. */
     Py_INCREF(xid);
-    self->tpc_xid = xid;
+    conn_set_xid(self, xid);
 
     return 0;
 }