[DuncanBentley]

GNU pr pads a column only to line up the next one, so a line never ends with spaces. uutils pads every cell, including the last one:

$ printf 'ab\nc\n' | pr -2 -t -w 9 -s'|' | od -c
GNU:    a b     |  c \n
uutils: a b     |  c       \n

This leaves the last cell of each row unpadded. In merge mode (-m), a file that has run out still gets its separator, as in GNU, and only the padding at the end of the line is dropped.

Most of the diff is the expected test output. I stripped the trailing spaces from the content lines of eight fixture files (column*.log.expected, mpr*.log.expected) and from the inline expectations in test_columns* and test_merge*. Nothing else in them changed. I checked the fixture commands against GNU pr: it prints no trailing spaces in any of them, apart from the -o offset on blank header lines (unchanged here) and the separators in merge mode.

I also added test_columns_last_column_not_padded.

This came up in review of #16078.

[sylvestre]

Thanks for your PR