BUG #14063: ALTER SYSTEM accepts 'newline' and renders itself inoperable.

The following bug has been logged on the website:

Bug reference: 14063
Logged by: Julian Schauder
Email address: julian(dot)schauder(at)credativ(dot)de
PostgreSQL version: 9.5.1
Operating system: Linux, Any
Description:

Howdy Hackers,

PostgreSQLs ALTER SYSTEM accepts a newline in its string-statements. This
will cause the postgresql.auto.conf to become unreadable and requires system
intervention (aka removal of the auto.conf)

postgres=# alter system set work_mem to '5MB
';
ALTER SYSTEM
Time: 37,718 ms
postgres=# alter system set work_mem to '5MB';
ERROR: could not parse contents of file "postgresql.auto.conf"
Time: 0,453 ms
postgres=# alter system reset work_mem ;
ERROR: could not parse contents of file "postgresql.auto.conf"
Time: 0,331 ms

According to code analysis i believe the easiest way around this is
tightening the value validation and ignore whitespaces or just remove
newline as a whitespace.

As this appears to be a new bug is relevant in all versions since ALTER
SYSTEM was introduced.

regards,
julian