I've been holding out on this forever because links to the latest are
occasionally useful, but more often than not, a permanent link to the
file as it currently stands is most useful. At any rate, it shouldn't
be Rhubarb's job to parse out the branch name.
Now that I've actually had time to assess things, it's clear this
parameter is only used as a way to convey the branch name and makes zero
sense. So, it's going to get dropped sooner or later.