Trim the file list for output.

def _trim_files(files, trim_output):
    '''
    Trim the file list for output.
    '''
    count = 100
    if not isinstance(trim_output, bool):
        count = trim_output

    if not(isinstance(trim_output, bool) and trim_output is False) and len(files) > count:
        files = files[:count]
        files.append("List trimmed after {0} files.".format(count))

    return files