pgsql-server: This patch adds an example to the CREATE DOMAIN docs.

Log Message:
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This patch adds an example to the CREATE DOMAIN docs.

David Fetter

Modified Files:
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pgsql-server/doc/src/sgml/ref:
create_domain.sgml (r1.17 -> r1.18)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/doc/src/sgml/ref/create_domain.sgml.diff?r1=1.17&r2=1.18)