pgsql: Document that libpq's PQntuples() might overflow.
Log Message:
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Document that libpq's PQntuples() might overflow.
Modified Files:
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pgsql/doc/src/sgml:
libpq.sgml (r1.245 -> r1.246)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/libpq.sgml?r1=1.245&r2=1.246)