BUG #10201: Invalid input accepted with IN expression

The following bug has been logged on the website:

Bug reference: 10201
Logged by: Daniel Baston
Email address: dbaston(at)gmail(dot)com
PostgreSQL version: 9.2.2
Operating system: Windows Server 2012
Description:

If two items in an IN expression are separated by a newline instead of a
comma, those items will be ignored with no error.

CREATE TABLE testing (id varchar(1));
INSERT INTO testing VALUES ('1'), ('2'), ('3'), ('4'), ('5');

-- Missing comma produces a syntax error
SELECT * FROM testing WHERE id IN ('1' '2', '3');

-- Unless there is a newline
SELECT * FROM testing WHERE id IN ('1'
'2', '3');

id
----
3
(1 row)