pgsql: Update conformance information about bigint type found by

Log Message:
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Update conformance information about bigint type

found by Michael Glaesemann

Modified Files:
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pgsql/doc/src/sgml:
datatype.sgml (r1.204 -> r1.205)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/datatype.sgml.diff?r1=1.204&r2=1.205)