The worker currently runs without configuration, but some of the new features

we're looking at will require it. In particular, the immediate need is that

PMD, a tool which we'll be adding, does not have a standard installation

mechanism, and often is run via a script from the download directory. The path

to this script has to be configured for the tool to work.
While I was in here, I fixed up the task serialization/accept config to get rid

of a big warning about accepting pickle content (which is insecure and going

away in future versions), and corrected the method of setting the broker URL,

which I hadn't noticed was incorrect because it defaults to localhost.

Ran the worker with and without a config file in place. Saw the expected

output, and that the (future) PMD tool loaded correctly.