Fix unsupported WatchForUpdates and build tags

Closes #105.

The `go1.1` constraint has been updated to `!go1.3` per
https://golang.org/pkg/go/build/#hdr-Build_Constraints and
https://github.com/go-fsnotify/fsnotify. Also, the existing call signature for
`WatchForUpdates()` in `watcher_unsupported.go` was stale.