#55 cygwin/iconv/sjis failure

[Shiro Kawai]

When compiled on cygwin with systems' iconv and sjis as the native CES, gettext tests fail.

This is because the check triggers conversion from iso8859-15 to sjis, which is not supported internally and falls back to iconv, where iconv uses strict Shift JIS instead of traditional sjis (=:= cp932).

Probably the best solution is to run internal conversion routine in 2-tier mode (iso8859-15 -> utf-8 -> sjis), since it makes conversions consistent. The overhead won't be much problem, since iconv also uses 2-tier conversion using ucs4 as the pivot.