Made Viewer ignore plugs with names starting "__".
Made Viewer ignore plugs with names starting "__".

This is the convention used elsewhere for internal plugs which shouldn't be presented to the user.

goddardl/gaffer,andrewkaufman/gaffer,GafferHQ/gaffer,ImageEngine/gaffer,chippey/gaffer,davidsminor/gaffer,ivanimanishi/gaffer,goddardl/gaffer,cedriclaunay/gaffer,appleseedhq/gaffer,andrewkaufman/gaffer,chippey/gaffer,cedriclaunay/gaffer,boberfly/gaffer,davidsminor/gaffer,ImageEngine/gaffer,lucienfostier/gaffer,hradec/gaffer,johnhaddon/gaffer,johnhaddon/gaffer,ivanimanishi/gaffer,boberfly/gaffer,GafferHQ/gaffer,chippey/gaffer,appleseedhq/gaffer,GafferHQ/gaffer,boberfly/gaffer,ImageEngine/gaffer,hradec/gaffer,davidsminor/gaffer,ivanimanishi/gaffer,ivanimanishi/gaffer,lucienfostier/gaffer,appleseedhq/gaffer,davidsminor/gaffer,goddardl/gaffer,lucienfostier/gaffer,andrewkaufman/gaffer,appleseedhq/gaffer,hradec/gaffer,goddardl/gaffer,johnhaddon/gaffer,hradec/gaffer,hradec/gaffer,johnhaddon/gaffer,chippey/gaffer,andrewkaufman/gaffer,johnhaddon/gaffer,cedriclaunay/gaffer,GafferHQ/gaffer,cedriclaunay/gaffer,andrewkaufman/gaffer,boberfly/gaffer,lucienfostier/gaffer,ImageEngine/gaffer,GafferHQ/gaffer