pgsql: Add some discussion of sort ordering to indices.sgml, which

Log Message:
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Add some discussion of sort ordering to indices.sgml, which curiously
had never touched the subject before.

Modified Files:
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pgsql/doc/src/sgml:
indices.sgml (r1.69 -> r1.70)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/indices.sgml.diff?r1=1.69&r2=1.70)