Performance Results on Windows

After almost a week of continuous measurements and 4320
individual data point, the results are in now. Summary:

* on cold disks, 'svn log -v' is 2x..3x as fast with packed f7 than with
  packed f6 in default config and up to 8x with advanced options
* on cold disks, 'svn export' with packed f7 is 40%.50% faster in
  default config and 2x as fast with advanced options
* ra_serf has an anomaly making "fast" config up to 100x slower
  than ra_svn - independent of repo format

Details to how I set up the repositories and measurements plus
the rationale behind it can be found in our wiki:

https://wiki.apache.org/subversion/MeasuringRepositoryPerformance

Tools and test script have been committed in r1610264. System
setup is close to what Ivan used in his tests, except for having
4GB to accommodate the much larger BSD repo as well.

Original measurement log and detailed results can be found in the
.zip file attached. The spreadsheet has been upgraded and now
displays f6/f7 because "+400%" is easier to understand than "-80%".
It now also highlights data cells with particularly high variation.

I'm currently waiting for the 'svnadmin dump' results to come in.
Those will take about 3 days but the expectation is that packed f7
may be slightly slower here due to the "unusual" access pattern.
After that, I'll try to isolate the trigger for the ra_serf anomaly.

-- Stefan^2.