Trailing slash

* made haruploader tolerate url's with a trailing slash
* unit tests for above
* editied test_config.yaml and changed url's to a single URL pointed at example.com, so the acceptance test runs faster and doesn't access edx.org.

/cc @clytwynec @benpatterson @jzoldak  
yea, agreed.
the problem is that the url joining is buried within the `save_file()` method of harpuloader, and not very testable.  It will take some refactoring of haruploader to make this actually testable. (not a bad thing, but a bit of work).