pgsql: Fix psql's \dD to show only one row per domain, even when the

Log Message:
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Fix psql's \dD to show only one row per domain, even when the domain has
multiple check constraints.

Modified Files:
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pgsql/src/bin/psql:
describe.c (r1.199 -> r1.200)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/bin/psql/describe.c?r1=1.199&r2=1.200)