Changed target_os from "win32" to "windows"

As of rust pull request 16435, cfg attributes now use "windows" instead
of "win32" for the target_os parameter.
Merge pull request #171 from inrustwetrust/windows-link-fix

Changed target_os from "win32" to "windows"
Merge pull request #173 from chuckries/master

fix cargo test after compiler removed shadowed usings.