Fix the create_index regression test for Danish collation.

In Danish collations, there are letter combinations which sort
higher than 'Z'.  A test for values > 'WA' was picking up rows
where the value started with 'AA', causing the test to fail.

Backpatch to 9.2, where the failing test was added.

Per report from Svenne Krap and analysis by Jeff Janes

src/test/regress/expected/create_index.out

@@ -2659,18 +2659,18 @@ CREATE INDEX dupindexcols_i ON dupindexcols (f1, id, f1 text_pattern_ops);
 ANALYZE dupindexcols;
 EXPLAIN (COSTS OFF)
   SELECT count(*) FROM dupindexcols
-    WHERE f1 > 'WA' and id < 1000 and f1 ~<~ 'YX';
-                                      QUERY PLAN                                       
----------------------------------------------------------------------------------------
+    WHERE f1 BETWEEN 'WA' AND 'ZZZ' and id < 1000 and f1 ~<~ 'YX';
+                                                   QUERY PLAN                                                   
+----------------------------------------------------------------------------------------------------------------
  Aggregate
    ->  Bitmap Heap Scan on dupindexcols
-         Recheck Cond: ((f1 > 'WA'::text) AND (id < 1000) AND (f1 ~<~ 'YX'::text))
+         Recheck Cond: ((f1 >= 'WA'::text) AND (f1 <= 'ZZZ'::text) AND (id < 1000) AND (f1 ~<~ 'YX'::text))
          ->  Bitmap Index Scan on dupindexcols_i
-               Index Cond: ((f1 > 'WA'::text) AND (id < 1000) AND (f1 ~<~ 'YX'::text))
+               Index Cond: ((f1 >= 'WA'::text) AND (f1 <= 'ZZZ'::text) AND (id < 1000) AND (f1 ~<~ 'YX'::text))
 (5 rows)
 
 SELECT count(*) FROM dupindexcols
-  WHERE f1 > 'WA' and id < 1000 and f1 ~<~ 'YX';
+  WHERE f1 BETWEEN 'WA' AND 'ZZZ' and id < 1000 and f1 ~<~ 'YX';
  count 
 -------
     97

src/test/regress/sql/create_index.sql

@@ -885,9 +885,9 @@ ANALYZE dupindexcols;
 
 EXPLAIN (COSTS OFF)
   SELECT count(*) FROM dupindexcols
-    WHERE f1 > 'WA' and id < 1000 and f1 ~<~ 'YX';
+    WHERE f1 BETWEEN 'WA' AND 'ZZZ' and id < 1000 and f1 ~<~ 'YX';
 SELECT count(*) FROM dupindexcols
-  WHERE f1 > 'WA' and id < 1000 and f1 ~<~ 'YX';
+  WHERE f1 BETWEEN 'WA' AND 'ZZZ' and id < 1000 and f1 ~<~ 'YX';
 
 --
 -- Check ordering of =ANY indexqual results (bug in 9.2.0)