BUG #5102: Silent IN (list of strings) failure to detect syntax error when list is linewrapped

The following bug has been logged online:

Bug reference: 5102
Logged by: Geoff Tolley
Email address: geoff(dot)tolley(at)yougov(dot)com
PostgreSQL version: 8.3.8
Operating system: Ubuntu 8.04 x86_64
Description: Silent IN (list of strings) failure to detect syntax
error when list is linewrapped
Details:

I would expect the last of these queries to give the same syntax error as
the penultimate one. Reproducible on my test instance of 8.4.1 as well:

postgres=# SELECT version();
version
----------------------------------------------------------------------------
---------------------
PostgreSQL 8.3.8 on x86_64-pc-linux-gnu, compiled by GCC cc (GCC) 4.2.4
(Ubuntu 4.2.4-1ubuntu3)
(1 row)

postgres=# SELECT 'hello' WHERE '1' IN ('1', '2');
?column?
----------
hello
(1 row)

postgres=# SELECT 'hello' WHERE '1' IN ('1' '2');
ERROR: syntax error at or near "'2'"
LINE 1: SELECT 'hello' WHERE '1' IN ('1' '2');
^
postgres=# SELECT 'hello' WHERE '1' IN ('1'
postgres(# '2');
?column?
----------
(0 rows)