Allow symlinks on Windows

[TravisCarden]

Now that we use rsync for file syncing on Windows, symlinks should work there, but they aren't officially supported yet for no other reason than that automated tests have not been created to prove that they work*. Create such tests and remove NoLinksExistOnWindows.

*To be precise, we have not yet been able to create a relative link on Windows to test with (absolute links are forbidden) due to an quirk of Windows that relative symlinks are actually created as absolute links most (if not all) of the time. Maybe it's not even possible, in which this issue can be closed.