pgsql: Add some more citext test cases, per David Wheeler.

Log Message:
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Add some more citext test cases, per David Wheeler. Also remove the
citext-to-and-from-xml tests, since those caused variation between
installations with or without libxml without really proving much. Instead
repurpose citext_1.out as the expected results in glibc en_US (and probably
other) locales.

Modified Files:
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pgsql/contrib/citext/expected:
citext.out (r1.4 -> r1.5)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/contrib/citext/expected/citext.out?r1=1.4&r2=1.5)
citext_1.out (r1.2 -> r1.3)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/contrib/citext/expected/citext_1.out?r1=1.2&r2=1.3)
pgsql/contrib/citext/sql:
citext.sql (r1.3 -> r1.4)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/contrib/citext/sql/citext.sql?r1=1.3&r2=1.4)