'Create a new dependency manager looking for packages under the paths listed
in `base_paths`.  The default base path is app.config.tool_dependency_dir.'

def __init__(self, default_base_path, conf_file=None, app_config={}):

    if (not os.path.exists(default_base_path)):
        log.warning("Path    '%s'    does    not    exist,    ignoring", default_base_path)
    if (not os.path.isdir(default_base_path)):
        log.warning("Path    '%s'    is    not    directory,    ignoring", default_base_path)
    self.__app_config = app_config
    self.default_base_path = os.path.abspath(default_base_path)
    self.resolver_classes = self.__resolvers_dict()
    self.dependency_resolvers = self.__build_dependency_resolvers(conf_file)
