python - lo: Align PGSERVICE handling with libpq.

Log Message:
-----------
Align PGSERVICE handling with libpq.

Formerly, if a service went unfound, ConfigParser would raise a
NoSectionError. This was done regardless of the file existence or readability,
which is inconsistent with libpq's error on access, but not on undefined service.
In the future, we will probably throw a warning about a missing service.

Additionally, allow users to specify the environment dictionary to get the
PGSYSCONFDIR variable from when using service options.

Modified Files:
--------------
    lo/postgresql/utility/client:
        environ.py (r1.1 -> r1.2)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/lo/postgresql/utility/client/environ.py.diff?r1=1.1&r2=1.2)
        option.py (r1.9 -> r1.10)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/lo/postgresql/utility/client/option.py.diff?r1=1.9&r2=1.10)