Increase the precision of comparison

[k0kubun]

I have a patch that consistently improves a benchmark by 0.5%. That, however, is rendered as 1.00 since "%.2f" % 1.005 returns that. Since we sometimes work on small optimizations, it might be useful to show one more number.

Before

-----  -----------  ----------  ----------  ----------  -------------  ------------
bench  before (ms)  stddev (%)  after (ms)  stddev (%)  after 1st itr  before/after
mail   69.8         0.4         69.4        0.2         1.00           1.00 
-----  -----------  ----------  ----------  ----------  -------------  ------------

After

-----  -----------  ----------  ----------  ----------  -------------  ------------
bench  before (ms)  stddev (%)  after (ms)  stddev (%)  after 1st itr  before/after
mail   69.8         0.4         69.4        0.2         1.004          1.005
-----  -----------  ----------  ----------  ----------  -------------  ------------