Return the field names (channel names) from dbf file fn. With
    usecols, return only names corresponding to the integers in
    usecols.

def channel_names(fn, usecols=None):
    """Return the field names (channel names) from dbf file fn. With
    usecols, return only names corresponding to the integers in
    usecols."""

    with open(fn, 'rb') as fo:
        names = dbfreader(fo).next()

    return usecols and [names[i] for i in usecols] or names