Show wxTestableFrame from its ctor

No real changes, just always show the frame as we need it to be shown for the
tests to run anyhow.

Also update the nonsensical comment about creating a hidden window just before
showing it.

tests/testableframe.cpp

@@ -20,6 +20,8 @@ wxTestableFrame::wxTestableFrame() : wxFrame(NULL, wxID_ANY, "Test Frame")
 {
     // Use fixed position to facilitate debugging.
     Move(200, 200);
+
+    Show();
 }
 
 void wxTestableFrame::OnEvent(wxEvent& evt)