pgsql: Suggest shell here-documents instead of psql -c for multiple com

Suggest shell here-documents instead of psql -c for multiple commands.

The documentation suggested using "echo | psql", but not the often-superior
alternative of a here-document.  Also, be more direct about suggesting
that people avoid -c for multiple commands.  Per discussion.

Branch
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REL9_1_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/e7cf0b89fbf6a0c6e2fa7ece01197e9b6d6f48d3

Modified Files
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doc/src/sgml/ref/psql-ref.sgml |   20 +++++++++++++++++---
1 file changed, 17 insertions(+), 3 deletions(-)