updated benchmark display/analysis code

[Martin Pool]

I updated the code previously written by Carl Friedrich Bolz to try to
make it more sensitive at detecting revisions which make substantial
changes to benchmark result (rather than experimental errors.)  I think
the new code does better but it is not very polished yet.  Nevertheless
it's available here 

https://code.launchpad.net/people/mbp/+branch/bzr-benchmark-display/mbp


-- 
Martin