bench: Use environ to run compares more than once

This will run the benchmarks the number of times specified by NODE_BENCH_RUNS,
to attempt to reduce variability.

If the number of runs is high enough, it'll also throw out the top and bottom
quartiles, since that's where the outliers will be.

It's not very fancy statistics-fu, but it's better than nothing.

Also, linted this file.  It had tabs in it.  TABS!