test for symlinks outside a watched parent dir

This test only matters for fsevents mode, so let me know if you want me to disable it for other modes to save time. Love to hear any other feedback you have as well.
Ah ok I see. So actually the labeling of this test should change to indicate the potential fault it's actually looking for. Something like 'should reuse watchers properly when following symlinks'.

But also, this watcher instance needs to be assigned to var and then closed at the end. Otherwise this watcher leaks and keeps running, potentially impacting other tests.