pgsql: Docs: document that psql's "\i -" means read from stdin.

Docs: document that psql's "\i -" means read from stdin.

This has worked that way for a long time, maybe always, but you would
not have known it from the documentation.  Also back-patch the notes
I added to HEAD earlier today about behavior of the "-f -" switch,
which likewise have been valid for many releases.

Branch
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REL9_3_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/818a680a6f0bc565cc12aaf9fa67752988b40f21

Modified Files
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doc/src/sgml/ref/psql-ref.sgml |   12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)