Polish up iswctype_test

• Split up the testcases into C locale and ja_JP.eucJP testcases.
• Avoid a segfault in the event that setlocale fails, similar to r290843
• Replace sizeof(x) / sizeof(*x) pattern with nitems(x)

MFC after: 1 week
X-MFC with: r290532
Sponsored by: EMC / Isilon Storage Division