The symlinks_works test is ignored on windows

[alexcrichton]

In #10179 I added support for symlinks bindings to libuv. I could never get the symlinks_work, so I'm ignoring it for now to get this patch landed.

This warrants further investigation, the problem I kept seeing was that a condition was raised saying "operation not permitted".

[klutzy]

Both libuv and libnative call CreateSymbolicLink API, which fails if user doesn't have some permission on the directories. (GetLastError() returns ERROR_PRIVILEGE_NOT_HELD on my machine)
Let's ignore the tests and add some notes on symlink document!

[steveklabnik]

libuv is totally gone now, so as far as I can tell, this needs closed.

[klutzy]

@steveklabnik the test is still at libstd/fs.rs. Could you reopen this?