[m-rev.] for post-commit review: speed up string.format for integers

[Zoltan Somogyi]

This diff takes the time to do 5 million string.formats
on my laptop from

27.950u 0.015s 0:27.98 99.9%	0+0k 0+0io 0pf+0w
27.266u 0.011s 0:27.29 99.9%	0+0k 0+8io 0pf+0w

to

18.191u 0.007s 0:18.21 99.8%	0+0k 0+0io 0pf+0w
17.988u 0.004s 0:18.00 99.8%	0+0k 0+0io 0pf+0w

I expect that the time taken to create the 5 million
random numbers is a significant fraction of the 18 seconds,
so the speedup is better than one-third.

Zoltan.
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