picking up bzr-usertest

[Martin Pool]

bzr-usertest is a macrobenchmark suite for bzr.

It has been quite useful in the past but it's also been semi-orphaned
since ianc left us, I think partly because it's a bit unobvious and
manual to get meaningful results out of it.

I'm going to pick it up and try to get it going again, with a short
term goal of making it tell you whether there is any significant
difference in performance between two versions of bzr (like tip vs
2.3).   There is some somewhat crufty code internally that's specific
to the csv format it currently produces, and on the whole I think it's
not worth keeping this: I'm going to just break it and replace it with
a more object oriented view of the results that will let us do more
stuff in process.

Martin