fix #394

this cleans up some system handles after openblas is finished with them, and doesn't disable ALL process privileges upon success. It also eliminates calls to `getenv` from `DllInit`, which [msdn documents as unsafe](http://msdn.microsoft.com/en-us/library/windows/desktop/dn633971(v=vs.85).aspx), and uses `GetEnvironmentVariable` directly instead

note: I am still waiting for confirmation that this works on all the user machines that originally reported the problem, but initial reports are very promising: [https://github.com/JuliaLang/julia/issues/5574](https://github.com/JuliaLang/julia/issues/5574)