Merge pull request #216 from pulp/mhrivnak-970267

970267 - removing the use of a parameter that didn't exist in python 2.6...
Merge pull request #217 from pulp/mhrivnak-970269

970269 - making the 'id' attribute of errata references optional, since ...
971138 - Add a new contents command to the CLI for ISO repos.
971138 - Include a missing module from my last commit.
Add some code comments.
Remove some unnecessary stray code.
Don't use self.__class__ in a super().
Use pulp.client.commands.options.OPTION_REPO_ID instead of 'repo-id'.
Merge branch 'rbarlow-iso-client-unit-list'