Fix symlink behaviour on kqueue

[arp242]

There were two problems here:

• When we see a link inside a directory the resolved version would get added to w.watches etc. but the link won't, resulting in many spurious create events for the link. This fixes Spurious symlink CREATE events on macOS when watching a directory #277; I'm surprised there aren't more reports for this).

• filepath.EvalSymlinks() will resolve any symlinks in the entire path, rather than just the link itself. This would cause paths such as:

  /path/to/LINK/dir/dir/WATCH-THIS
  

  To have the wrong Event.Name; many of the test cases failed because of this because /tmp is a link to /private/tmp on macOS, but curiously no one reported it AFAIK (I guess many people don't use symlinks all that much).

  Example:

  % mkdir /tmp/xxx
  % touch /tmp/xxx/FILE
  
  % ln -s /tmp/xxx/LINK /tmp/xxx/FILE   # 25 years of Unix experience, and still...
  ln: /tmp/xxx/FILE: File exists
  % ln -s /tmp/xxx/FILE /tmp/xxx/LINK
  

  Before it would do:

  % go run ./cmd/fsnotify watch /tmp/xxx &
  % touch /tmp/xxx/FILE
  03:23:03.2731   1 CHMOD         "/private/tmp/xxx/FILE"
  03:23:03.2744   2 CHMOD         "/tmp/xxx/FILE"
  ^C
  
  % fsnotify watch /tmp/xxx/LINK &
  % touch /tmp/xxx/LINK
  03:26:37.3576   1 CHMOD         "/private/tmp/xxx/FILE"
  

  And now it does:

  % go run ./cmd/fsnotify watch /tmp/xxx &
  03:23:47.8911   1 CHMOD         "/tmp/xxx/FILE"
  ^C
  
  % fsnotify watch /tmp/xxx/LINK &
  % touch /tmp/xxx/LINK
  03:27:38.5227   1 CHMOD         "/tmp/xxx/FILE"
  

[arp242]

Still got some build failures in CI.

macOS 11 (after restart it did work):

--- FAIL: TestWatchSymlink/277 (1.18s)
    fsnotify_test.go:558: 
        have:
        	CREATE               "/foo"
        	WRITE                ""
        	WRITE                ""
        	WRITE                ""
        	REMOVE               "/foo"
        	CREATE               "/apple"
        	CREATE               "/pear"
        	REMOVE|RENAME        "/apple"
        	REMOVE               "/pear"
        want:
        	CREATE               "/foo"
        	REMOVE               "/foo"
        	CREATE               "/apple"
        	CREATE               "/pear"
        	REMOVE|RENAME        "/apple"
        	REMOVE               "/pear"

FreeBSD:

        	CREATE               "/foo"
        	REMOVE               "/foo"
        	CREATE               "/apple"
        	CREATE               "/pear"
        	REMOVE|RENAME        "/apple"
        	REMOVE               "/pear"
        	REMOVE|WRITE         ""
        	CREATE               "."

        	# After restart
        	CREATE               "/foo"
        	REMOVE               "/foo"
        	CREATE               "/apple"
        	CREATE               "/pear"
        	REMOVE|RENAME        "/apple"
        	REMOVE               "/pear"

NetBSD:

        	CREATE               "/foo"
        	REMOVE               "/foo"
        	CREATE               "/apple"
        	REMOVE|RENAME        "/apple"

        	# After restart
        	CREATE               "/foo"
        	REMOVE               "/foo"
        	CREATE               "/apple"
        	CREATE               "/pear"
        	REMOVE|RENAME        "/apple"
        	REMOVE               "/pear"