pr: treat a page length of exactly 10 as omitting the header

[luantaraschi]

pr --help states the rule twice, under -l and under -t: a page length of
10 or less implies -t. pr applies it at < 10 instead, so a page length of
exactly 10 keeps the header and the trailer and then subtracts them from the
page, leaving zero lines for content.

With three lines of input, against GNU coreutils 9.7:

command	GNU	before	after
pr -l 10 -h hdr	the 3 lines	3 empty pages, 30 lines, no content	the 3 lines
pr -l 10 -t	the 3 lines	nothing at all	the 3 lines
pr -l 10 -T	the 3 lines	nothing at all	the 3 lines
pr -l 9 or pr -l 11	unchanged	unchanged	unchanged

The -t case drops the input on the floor and still exits 0.

The variable already carries the intended rule in its name, page_length_le_ht,
so this is the comparison catching up with it.

Two differences at -l 10 are not part of this and are still there afterwards:
-F emits a trailing form feed that GNU does not, and -2 lays the columns out
differently. Both reproduce without any -l at all.

Checked against GNU for page lengths 1, 2, 5, 9, 10, 11, 12, 20 and 66, with
-h, -t, -T, -n, -d and -m, on a 3 line and a 40 line input.

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[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/date/resolution (fails in this run but passes in the 'main' branch)
Note: The gnu test tests/env/env-signal-handler was skipped on 'main' but is now failing.
Skip an intermittent issue tests/tail/tail-n0f (was skipped on 'main', now failing)

[codspeed-hq]

Merging this PR will degrade performance by 4.01%

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

❌ 1 regressed benchmark
✅ 356 untouched benchmarks
⏩ 50 skipped benchmarks¹

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Simulation	du_summarize_balanced_tree[(5, 4, 10)]	16.1 ms	16.8 ms	-4.01%

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

---

_{Comparing luantaraschi:fix/pr-page-length-10 (86618a2) with main (a5a7249)}

Footnotes

1. 50 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

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[cakebaker]

Thanks for your PR!