From: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
      Michal Rokos <m.rokos@sh.cvut.cz>

The problem is: even if vfat_striptail_len() counts len of name without
trailing dots and sets len to the correct value, utf8_mbstowcs() doesn't
care about len and takes whole name.  So dirs and files with dots can be
created on vfat fs.