'Return a newest-to-oldest list of distributions for `project_name`'

def __getitem__(self, project_name):

    try:
        return self._cache[project_name]
    except KeyError:
        project_name = project_name.lower()
        if (project_name not in self._distmap):
            return []
    if (project_name not in self._cache):
        dists = self._cache[project_name] = self._distmap[project_name]
        _sort_dists(dists)
    return self._cache[project_name]
