Ready event not working on composeWatcher

[Timo Tijhof]

During #73, I was adding on('ready') to various tests, and they worked everywhere, except for the two tests that use composeWatcher.

Waiting for ready on a composed watcher times out, because I forgot to add support for it in #71. I did not realise...

I can fix this, but wanted to focus on #69 first, so I'm writing it down here for later :)

[Yuan Chuan]

I'll handle this if I have time in the following days :D