doc/go1.3.txt: mention windows syscall.NewCallbackCDecl
doc/go1.3.txt: mention windows syscall.NewCallbackCDecl

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https://codereview.appspot.com/44160044

apparentlymart/golang,apparentlymart/golang,apparentlymart/golang,apparentlymart/golang,apparentlymart/golang,apparentlymart/golang,apparentlymart/golang