Changed to inherit from PointProbe.  Fixed the access to conductances from the layer.  Now uses getConductance.
Changed to inherit from PointProbe.  Fixed the access to conductances from the layer.  Now uses getConductance.

git-svn-id: 602a26e73ae9f2a14e2bb95676f2e137fcc39919@3406 7c0444ca-5550-0410-9008-faecdbe78eb5

dpaiton/OpenPV,dpaiton/OpenPV,dpaiton/OpenPV,PetaVision/OpenPV,dpaiton/OpenPV,PetaVision/OpenPV,dpaiton/OpenPV,dpaiton/OpenPV,PetaVision/OpenPV,dpaiton/OpenPV,dpaiton/OpenPV,PetaVision/OpenPV,PetaVision/OpenPV