Apply patches from kuroda/iso-2022-jp

These patches introduce some special treatments for ISO-2022-JP
encoding (so-called JIS-code), which is the de facto standard
when we send an email written in Japanese language.

These patches have effects only when a Mail object is
instanciated with :charset => 'ISO-2022-JP' option.
With this option, the header values and body text are
automatically converted from UTF-8 to ISO-2022-JP.

Note that some characters are replaced with other
characters before this conversion takes place
in order to solve problems on some platforms.

See https://github.com/kuroda/mail-iso-2022-jp for details.