* ext/iconv/iconv.c (iconv_fail): just yield error and return the
result if a block is given.
* ext/iconv/iconv.c (iconv_convert): yield error and append the
result if a block is given.
* ext/iconv/charset_alias.rb (charset_alias): optional third
argument.
* ext/iconv/charset_alias.rb (charset_alias): use CP932 instead of
SHIFT_JIS on cygwin.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@4476 b2dd03c8-39d4-4d8f-98ff-823fe69b080e