Make contrib regression tests safe for Danish locale.

In btree_gin and citext, avoid some not-particularly-interesting
dependencies on the sorting of 'aa'.  In tsearch2, use COLLATE "C" to
remove an uninteresting dependency on locale sort order (and thereby
allow removal of a variant expected-file).

Also, in citext, avoid assuming that lower('I') = 'i'.  This isn't relevant
to Danish but it does fail in Turkish.

contrib/btree_gin/expected/bytea.out

@@ -4,13 +4,13 @@ SET bytea_output TO escape;
 CREATE TABLE test_bytea (
 	i bytea
 );
-INSERT INTO test_bytea VALUES ('aaa'),('a'),('abc'),('abb'),('axy'),('xyz');
+INSERT INTO test_bytea VALUES ('a'),('ab'),('abc'),('abb'),('axy'),('xyz');
 CREATE INDEX idx_bytea ON test_bytea USING gin (i);
 SELECT * FROM test_bytea WHERE i<'abc'::bytea ORDER BY i;
   i  
 -----
  a
- aaa
+ ab
  abb
 (3 rows)
 
@@ -18,7 +18,7 @@ SELECT * FROM test_bytea WHERE i<='abc'::bytea ORDER BY i;
   i  
 -----
  a
- aaa
+ ab
  abb
  abc
 (4 rows)