'Classify from the path *filename* only.
Sets `lang\' and `langinfo\', if can be determined.'

def _classify_from_filename(self, lidb, env):

    filename = basename(self.path)
    if (env is not None):
        li = env.langinfo_from_filename(filename)
        if li:
            log.debug("lang    from    env:    `%s'    ->    `%s'", filename, li.name)
            self.langinfo = li
            self.lang = li.name
            self.is_text = li.is_text
            return
    idx = 0
    while True:
        idx = filename.find('.', idx)
        if (idx == (-1)):
            break
        ext = filename[idx:]
        li = lidb.langinfo_from_ext(ext)
        if li:
            log.debug("lang    from    ext:    `%s'    ->    `%s'", ext, li.name)
            self.langinfo = li
            self.lang = li.name
            self.is_text = li.is_text
            return
        idx += 1
    li = lidb.langinfo_from_filename(filename)
    if li:
        log.debug("lang    from    filename:    `%s'    ->    `%s'", filename, li.name)
        self.langinfo = li
        self.lang = li.name
        self.is_text = li.is_text
        return
