pgsql: Teach CREATE CONSTRAINT TRIGGER to convert old-style foreign key

Log Message:
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Teach CREATE CONSTRAINT TRIGGER to convert old-style foreign key
trigger definitions into regular foreign key constraints.  This seems
necessary given that some people evidently never did get around to
running adddepend on their schemas, and without some sort of hack the
old definitions will no longer work.  Per report from Olivier Prenant
and subsequent investigation.

Modified Files:
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    pgsql/src/backend/commands:
        trigger.c (r1.219 -> r1.220)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/trigger.c?r1=1.219&r2=1.220)