pageinspect: Make btree test more portable

Choose test data that makes the output independent of endianness and
alignment.

contrib/pageinspect/expected/btree.out

@@ -1,5 +1,5 @@
-CREATE TABLE test1 (a int, b text);
-INSERT INTO test1 VALUES (1, 'one');
+CREATE TABLE test1 (a int8, b text);
+INSERT INTO test1 VALUES (72057594037927937, 'text');
 CREATE INDEX test1_a_idx ON test1 USING btree (a);
 \x
 SELECT * FROM bt_metap('test1_a_idx');
@@ -38,7 +38,7 @@ ctid       | (0,1)
 itemlen    | 16
 nulls      | f
 vars       | f
-data       | 01 00 00 00 00 00 00 00
+data       | 01 00 00 00 00 00 00 01
 
 SELECT * FROM bt_page_items('test1_a_idx', 2);
 ERROR:  block number out of range

contrib/pageinspect/sql/btree.sql

@@ -1,5 +1,5 @@
-CREATE TABLE test1 (a int, b text);
-INSERT INTO test1 VALUES (1, 'one');
+CREATE TABLE test1 (a int8, b text);
+INSERT INTO test1 VALUES (72057594037927937, 'text');
 CREATE INDEX test1_a_idx ON test1 USING btree (a);
 
 \x