Use os.path.join to create outputXmlChangeLogFilePath.
Invoke path join and split as os.path.join and os.path.split for code readability (join and split are too generic by themselves)
Fixed unwanted re-execution of previously-executed ChangeSets by using logicalFilePath attribute in databaseChangeLog. This fixes issue #13.
Added a strong WARNING comment in changeset.py about the need to persist the generated databaseChangeLog/changeSet content in order to avoid re-execution of previously-executed changesets.
Changed single-quotes to double-quotes in changeset.py per Numenta coding guidelines.
Use p.communicate() BEFORE p.wait() to avoid deadlock in case the process spits out more STDERR/STDOUT data than there is room for in the pipe's buffer (which is not that large)