Fixes to allow the Mf.test_mf_auto_analysis system test to pass on Mac OS X.

The simulated event.GetPosition() method in the Fake_right_click class the file
test_suite/gui_tests/model_free.py must return a wx.Point object and not a Python tuple.  The
gui.components.base_list.Base_list.on_right_click() method has also been modified with a wx.Yield()
call to allos the test to pass.