group and user asserts don't work on Windows

[juliandunn]

The group and user asserts don't work on Windows, because the Etc library on Windows isn't going to return anything. So an assertion like:

    directory("C:\\inetpub\\wwwroot").must_exist.with(:owner, "Administrator")

always returns

The directory C:\inetpub\wwwroot does not have the expected owner.
Expected: "Administrator"
  Actual: nil

Indeed, Etc.getpwnam("Administrator") on Windows returns nil under irb.

[calavera]

Unfortunately, that's either a Chef or a Ruby bug. We only use the resources that Chef makes available.