Fix testlibpq3

The sample output assumes non-standard-conforming interpretation of
backslashes in input literals, so the actual output didn't match.

Noticed while perusing another patch that touches this file.

Evidently this code is seldom checked, so I'm not going to bother
backpatching this fix.

src/test/examples/testlibpq3.c

@@ -11,8 +11,8 @@
  * CREATE SCHEMA testlibpq3;
  * SET search_path = testlibpq3;
  * CREATE TABLE test1 (i int4, t text, b bytea);
- * INSERT INTO test1 values (1, 'joe''s place', '\\000\\001\\002\\003\\004');
- * INSERT INTO test1 values (2, 'ho there', '\\004\\003\\002\\001\\000');
+ * INSERT INTO test1 values (1, 'joe''s place', '\000\001\002\003\004');
+ * INSERT INTO test1 values (2, 'ho there', '\004\003\002\001\000');
  *
  * The expected output is:
  *

src/test/examples/testlibpq3.sql

 CREATE SCHEMA testlibpq3;
 SET search_path = testlibpq3;
+SET standard_conforming_strings = ON;
 CREATE TABLE test1 (i int4, t text, b bytea);
-INSERT INTO test1 values (1, 'joe''s place', '\\000\\001\\002\\003\\004');
-INSERT INTO test1 values (2, 'ho there', '\\004\\003\\002\\001\\000');
+INSERT INTO test1 values (1, 'joe''s place', '\000\001\002\003\004');
+INSERT INTO test1 values (2, 'ho there', '\004\003\002\001\000');