[io] Apply patch from Andrew Whitworth in RT #51990.  wknight8111++ * silence some warnings on win32. * update documentation on error return value.
[io] Apply patch from Andrew Whitworth in RT #51990.  wknight8111++
* silence some warnings on win32.
* update documentation on error return value.


git-svn-id: 6e74a02f85675cec270f5d931b0f6998666294a3@26521 d31e2699-5ff4-0310-a27c-f18f2fbe73fe

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