Fixes issue 1571:

Adding missing close for open.
If the "close()" call is missing after a "open(filename)" call, the filename isn't guaranteed to be closed before the interpreter exits.
This is generally a bad practice as explained here: https://stackoverflow.com/questions/7395542/is-explicitly-closing-files-important

Also replaced "fid=open(filename) fid.close()" statements for files with the safer
"with open(filename) as fid:" blocks. See https://www.python.org/dev/peps/pep-0343/

demo/ScrolledMessageDialog.py

@@ -15,9 +15,8 @@ class TestPanel(wx.Panel):
 
 
     def OnButton(self, evt):
-        f = open("Main.py", "r")
-        msg = f.read()
-        f.close()
+        with open("Main.py", "r") as f:
+            msg = f.read()
 
         dlg = wx.lib.dialogs.ScrolledMessageDialog(self, msg, "message test")
         dlg.ShowModal()