eat output when checking for python module

git-svn-id: https://svn.salilab.org/imp/trunk@16709 e91f8c7b-0e32-4433-a9ac-4502d39a4eab
disable em2d if no usable opencv is found

git-svn-id: https://svn.salilab.org/imp/trunk@16710 e91f8c7b-0e32-4433-a9ac-4502d39a4eab