Benchmark.t: disdplay calibration diag output

When the notorious test 15 fails, show the ratio of our earlier 3sec and
1sec calibration in the diag output.
Benchmark.t: consistent delta comparing

when we compare the number of iterations done in 3 seconds with
3 * (the number of iterations done in 1 second), the comparison's
effective delta of toleration depended on which value was larger:
if a > b, it tested for a/b <= 1.666; if b > a, it tested for b/a < 1.4.

Make it consistently 1.4 (or 1+$DELTA to be precise).