Implements the actual version setup() keyword.

def version_keyword(dist, attr, value):
    """
    Implements the actual version setup() keyword.
    """
    if value == "PBR":
        from pbr.util import setup_cfg_to_setup_kwargs

        path = "setup.cfg"
        parser = ConfigParser()
        if not os.path.exists(path):
            raise ValueError("file '%s' does not exist" % os.path.abspath(path))
        parser.read(path)
        config = {}
        for section in parser.sections():
            config[section] = dict(parser.items(section))
        attrs = setup_cfg_to_setup_kwargs(config)
        version = str(Version(attrs["name"]))
        os.environ["PBR_VERSION"] = version
    else:
        version = str(Version(dist.metadata.get_name()))
    dist.metadata.version = version