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/

unittests/test_lib_pubsub_provider.py

@@ -89,9 +89,8 @@ class lib_pubsub_Except(wtc.PubsubTestCase):
                             pass
             """
 
-        myTopicTree = open('myTopicTree.py', 'w')
-        myTopicTree.write(dedent(provFile))
-        myTopicTree.close()
+        with open('myTopicTree.py', 'w') as myTopicTree:
+            myTopicTree.write(dedent(provFile))
         self.pub.addTopicDefnProvider('myTopicTree',
                                       format=self.pub.TOPIC_TREE_FROM_MODULE)
         import os