Use inotify to reload dependent files on change only

[ejv2]

Rather than using a continuous reload loop to reload the queue file, instead wait for events delivered from the kernel using inotify - falling back to periodic reloads if the API is unavailable or unusable (for instance on some BSDs).

[ejv2]

This is more awkward than it initially appeared because of cross platforming stuff. The libraries which offer this with a wrapper around cgo all seem to be quite platform dependent and I would like to avoid that.

Until I've figured this out more I'm excluding it from v4.0