Merge global configuration with user's personal configuration.

    Global configuration has always higher priority.

def conf_merger(user_dict, variable):
    """
    Merge global configuration with user's personal configuration.

    Global configuration has always higher priority.
    """
    if variable not in globals().keys():
        raise NameError("Unknown variable '%s'." % variable)

    if variable not in user_dict:
        return globals()[variable]

    return globals()[variable] and user_dict[variable]