detect proxy settings) had the wrong logic for detecting
if the checkbox 'Exclude simple hostnames' is checked. This
checkin fixes that.

As a result the test failure 'Issue8455' goes away on systems
where the checkbox is not checked.

I'm carefully avoiding saying that is fixes that issue,
test_urllib2_localnet assumes that system proxy settings are
empty (not just on OSX, see Issue8455 for details).