python - lo: Don't rely on os.getlogin for getting a good default

Log Message:
-----------
Don't rely on os.getlogin for getting a good default username.

The 'getpass.getuser' function seems to be the sanctioned facility in which to
resolve the current username.

Per pg_slythe issue reported by Adrian Klaver.

Modified Files:
--------------
lo/postgresql/utility/client:
option.py (r1.2 -> r1.3)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/lo/postgresql/utility/client/option.py.diff?r1=1.2&r2=1.3)