fix op/infnan.t failures on VC 6

fixes 2 failures, first is a fatal error, sceond is a not ok
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ok 460 - abs(NaN) is NaN
ok 461 - int(NaN) is NaN
Can't take sqrt of NaN at op/infnan.t line 319.
C:\perl521\srcvc6\t>
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ok 465 - sin(NaN) is NaN
not ok 466 - rand(NaN) is NaN
# Failed test 466 - rand(NaN) is NaN at op/infnan.t line 331
#      got "0.20653527722801"
# expected "NaN"
ok 467 - sin(9**9**9) is NaN
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improve and reword README.win32