BUG: Fix CERTIFICATE_VERIFY_FAILED error using "urllib2.urlopen()" on MacOSX

See http://www.na-mic.org/Bug/view.php?id=4067

This commit ensures the "Slicer.crt" certificate is found when using
function like "urlib2.urlopen()" in the python interactor from an install
tree on MacOSX.

This is needed because on MacOSX the launcher is not used when the
application is installed.

Reported-by: Andriy Fedorov <fedorov@bwh.harvard.edu>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@24662 3bd1e089-480b-0410-8dfb-8563597acbee