Code review comment for lp:~leonardr/lazr.restful/multiversion-destructors

This branch adds multi-version error checking for destructor methods. A destructor method cannot have any arguments that are not fixed to specific values. The previous code was not version-aware, so it was only checking for the most recent version of the web service. In this branch I check every version in which the destructor method is published.

I also defined a tiny helper method, _version_name, which takes care of this logic which I was putting all over the place when printing out error messages:

    if version is None:
        version = "(earliest version)"