Reduce unnecessary 2.7 versus 3.4+ differences in idlelib/configDialog.py.

2009-02-02 51562 (27c589f09a21) merged Mac support revisions into 3.0.
2009-03-04 52014 (dc3d24824b60) merged slightly improved version into 2.7.
Change 3.4+ to match the later 2.7 patch.  Buttons tested manually.