Add new test conf keys found when merging timings files
Don't always mix test score into summary + bug fix in summary score calc

Some tests, such as empty loops, don't represent a structure that
would ever appear in real code but which can be very heavily optimized
by some compilers, thus skewing summary scores unrealistically.  This
change provides a way for tests to be opted-out of the summary score.

Also, fix a bug where the geometric mean would use a power calculated
for *all* tests, not just the ones actually included in the summary
score (which has been inaccurate ever since incomplete results were
auto-skipped).
Opt out several microbenchmarks from summary score calculations