Use PyThreadState_DeleteCurrent() instead of PyThreadState_Delete()

and PyEval_ReleaseThread().

This fixes SF bug #125673 PyThreadState_Delete: invalid tstate (Unix
only?).

Modules/threadmodule.c

@@ -204,8 +204,7 @@ t_bootstrap(void *boot_raw)
 	else
 		Py_DECREF(res);
 	PyThreadState_Clear(tstate);
-	PyEval_ReleaseThread(tstate);
-	PyThreadState_Delete(tstate);
+	PyThreadState_DeleteCurrent();
 	PyThread_exit_thread();
 }