Method that calculates all the configuration files that are valid, according to the
        'set_paths' and other methods for this module.

def existing_config_files():
    """
        Method that calculates all the configuration files that are valid, according to the
        'set_paths' and other methods for this module.
    """
    global _ETC_PATHS
    global _MAIN_CONFIG_FILE
    global _CONFIG_VAR_INCLUDE
    global _CONFIG_FILTER

    config_files = []
    for possible in _ETC_PATHS:
        config_files = config_files + glob.glob("%s%s" % (possible, _MAIN_CONFIG_FILE))
    
    if _CONFIG_VAR_INCLUDE != "":
        main_config = Configuration("general", {
            _CONFIG_VAR_INCLUDE:""
        }, _MAIN_CONFIG_FILE)

        if main_config.CONFIG_DIR != "":
            for possible in _ETC_PATHS:
                config_files = config_files + glob.glob("%s%s/%s" % (possible, main_config.CONFIG_DIR, _CONFIG_FILTER))
            
    return config_files