BUG #7514: postgres -k no longer works with spaces in the path

The following bug has been logged on the website:

Bug reference: 7514
Logged by: Murray Cumming
Email address: murrayc(at)murrayc(dot)com
PostgreSQL version: 9.1.5
Operating system: Fedora Linux 17
Description:

At some point, probably in 9.1.5, the -k option to Postgres ("Unix-domain
socket location" in --help), stopped accepting paths that contain spaces.

For instance,
-k '/tmp/testglom2FPDKW/path with spaces/some_postgres_data'

It now fails with this error:
FATAL: invalid list syntax for "unix_socket_directories"

This is not critical, but it showed up in the regression tests for Glom. And
users are fairly likely to use paths with spaces.

-k apparently accepts a comma-separated list, so there should be no need to
check for spaces.