Log Message:
-----------
Reword exclusion constriants to mention that the operator can return
false or null, per Tom.
Modified Files:
--------------
pgsql/doc/src/sgml:
ddl.sgml (r1.92 -> r1.93)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ddl.sgml?r1=1.92&r2=1.93)