pgsql: Improve psql \?'s description of large-object-related commands.

Improve psql \?'s description of large-object-related commands.

Provide a gloss of which command does what, as all other backslash
commands have.  Put the large-object command section into a more
considered spot in the list.

In passing, update the output-lines count in helpVariables()
(oversight in 7844c9918, looks like).

Thibaud Walkowiak, reviewed by Nathan Bossart and myself

Discussion: https://postgr.es/m/43f0439c-df3e-a045-ac99-af33523cc2d4@dalibo.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/1fbe94084fd34200e61dd1db6225e8c8c65c000d

Modified Files
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src/bin/psql/help.c | 19 ++++++++++---------
1 file changed, 10 insertions(+), 9 deletions(-)