pgsql: Teach deparsing of CASE expressions to cope with the simplified

Log Message:
-----------
Teach deparsing of CASE expressions to cope with the simplified forms
that simplify_boolean_equality() may leave behind.  This is only relevant
if the user writes something a bit silly, like CASE x=y WHEN TRUE THEN.
Per example from Michael Fuhr; may or may not explain bug #2106.

Modified Files:
--------------
    pgsql/src/backend/utils/adt:
        ruleutils.c (r1.209 -> r1.210)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/ruleutils.c.diff?r1=1.209&r2=1.210)