add GetOSName support for Windows 8.1

Adds support to GetOSName() for Windows 8.1.

The 2012 R2 entry is based on the table at http://msdn.microsoft.com/en-us/library/windows/desktop/ms724833%28v=vs.85%29.aspx

Tested on Windows 8.1 Pro, Windows 7 Pro in a cygwin build (this is one of the tests causing my cygwin perl smokes to fail.)

This doesn't attempt to fix cpan #90807