The common style is to pad to 4 digits.
Running the current perl scripts to generate these map files would override
this change, but the next commit will rewrite the perl scripts to produce
this style. I'm doing this as a separate commit, to make it more clear what
non-cosmetic changes the next commit makes to the map files.
Discussion: https://postgr.es/m/08e7892a-d55c-eefe-76e6-7910bc8dd1f3@iki.fi
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