skip if Converter is not found
POSIX Text File must end with eol

http://pubs.opengroup.org/onlinepubs/000095399/basedefs/xbd_chap03.html#tag_03_392
Use \A and \z to see whole string

^ is the begining of the line
\A is the beginning of the string
$ is the end of the line
\z is the end of the string

RegexpM17N.non_empty? seems to check the whole string
There's no characters

This must be more speedy because it will fail when it find a string.
Regexp#=~ is the Ruby Way
skip if dummy encodings

dummy encodings like
* UTF-16 has BOM. Note that
* UTF-32: ditto.
* ISO-2022-JP: a stateful encoding
are hard to use as a internal encoding.
convert encoding of the source of regexp
speed up
non empty means its length is larger than zero
non empty means not empty