Don't refer to the database name "regression" inside the regression test

scripts, to allow running the test successfully with another database name.

src/test/regress/expected/prepare.out

@@ -58,10 +58,10 @@ SELECT name, statement, parameter_types FROM pg_prepared_statements;
 PREPARE q2(text) AS
 	SELECT datname, datistemplate, datallowconn
 	FROM pg_database WHERE datname = $1;
-EXECUTE q2('regression');
+EXECUTE q2('postgres');
  datname  | datistemplate | datallowconn 
-------------+---------------+--------------
- regression | f             | t
+----------+---------------+--------------
+ postgres | f             | t
 (1 row)
 
 PREPARE q3(text, int, float, boolean, oid, smallint) AS

src/test/regress/expected/privileges.out

@@ -582,7 +582,7 @@ SELECT has_table_privilege('regressuser1', 'atest4', 'SELECT WITH GRANT OPTION')
 (1 row)
 
 -- clean up
-\c regression
+\c
 DROP FUNCTION testfunc2(int);
 DROP FUNCTION testfunc4(boolean);
 DROP VIEW atestv1;

src/test/regress/expected/temp.out

@@ -42,7 +42,7 @@ SELECT * FROM temptest;
 DROP TABLE temptest;
 -- test temp table deletion
 CREATE TEMP TABLE temptest(col int);
-\c regression
+\c
 SELECT * FROM temptest;
 ERROR:  relation "temptest" does not exist
 -- Test ON COMMIT DELETE ROWS

src/test/regress/sql/prepare.sql

@@ -34,7 +34,7 @@ PREPARE q2(text) AS
 	SELECT datname, datistemplate, datallowconn
 	FROM pg_database WHERE datname = $1;
 
-EXECUTE q2('regression');
+EXECUTE q2('postgres');
 
 PREPARE q3(text, int, float, boolean, oid, smallint) AS
 	SELECT * FROM tenk1 WHERE string4 = $1 AND (four = $2 OR

src/test/regress/sql/privileges.sql

@@ -334,7 +334,7 @@ SELECT has_table_privilege('regressuser1', 'atest4', 'SELECT WITH GRANT OPTION')
 
 -- clean up
 
-\c regression
+\c
 
 DROP FUNCTION testfunc2(int);
 DROP FUNCTION testfunc4(boolean);

src/test/regress/sql/temp.sql

@@ -47,7 +47,7 @@ DROP TABLE temptest;
 
 CREATE TEMP TABLE temptest(col int);
 
-\c regression
+\c
 
 SELECT * FROM temptest;