Supervisors should be able to start up with `Haste::Quickly`

[jjl]

At the moment, they panic if you set them to quickly, so I wouldn't advise configuring them this way.

I had an initial go at it this morning, but I ran across problems trying to update Start::start(). It's clearly going to require more thought and a bit of rearrangement, but sigh, i quite liked this api.

I don't expect this is actually much of a limitation in practice, but I'd like to fix it. Or for someone else to fix it :)