Windows: fix uname on recent Windows versions
Correctly identify Windows 8.1, Windows 10, and Windows Server 2008 and later from their NT versions. On recent Windows versions, the GetVersionEx() function may report an earlier Windows version than the running OS. To avoid user confusion, add "[or later]" to Tor's version string on affected versions of Windows. Remove Windows versions that were never supported by the GetVersionEx() function. Stop duplicating the latest Windows version in get_uname(). Fixes bug 28096; bugfix on 0.2.2.34; reported by Keifer Bly.