Code review comment for lp:~leonardr/lazr.restful/no-latest-version

This branch fixes bug 520542, removing the confusing "latest_version_uri_prefix" attribute from IWebServiceConfiguration and everywhere else. Now there is a single list of active_versions and if you want to have a floating dev version, it can go on the end of the active_versions list.

The changes to the tests happen because FakeRequest (used by the tests) by default made a request to the last version mentioned in active_versions, *not* the most recent version period. When 'devel' was in latest_version_uri_prefix, the last version mentioned in active_versions was '1.0'. Now it's 'devel', so some of the URLs in tests changed.