Add DrakeFunctionConstraint.
Add DrakeFunctionConstraint.

This class will eventually replace Constraint, but for now it allows us to
merge in new DrakeFunction features without disrupting our Constraint
infrastructure.

hanssusilo/drake,sheim/drake,billhoffman/drake,hanssusilo/drake,edowson/drake,tkoolen/drake,crogers3/drake,hanssusilo/drake,billhoffman/drake,scottviteri/drake,psiorx/drake,astrorog/drake,astrorog/drake,scottviteri/drake,tkoolen/drake,billhoffman/drake,edowson/drake,crogers3/drake,astrorog/drake,scottviteri/drake,sheim/drake,billhoffman/drake,psiorx/drake,sheim/drake,sheim/drake,manuelli/drake,manuelli/drake,thientu/drake,manuelli/drake,astrorog/drake,psiorx/drake,billhoffman/drake,thientu/drake,scottviteri/drake,crogers3/drake,manuelli/drake,scottviteri/drake,hanssusilo/drake,edowson/drake,crogers3/drake,psiorx/drake,hanssusilo/drake,psiorx/drake,sheim/drake,thientu/drake,astrorog/drake,psiorx/drake,billhoffman/drake,scottviteri/drake,tkoolen/drake,edowson/drake,psiorx/drake,astrorog/drake,scottviteri/drake,manuelli/drake,hanssusilo/drake,thientu/drake,hanssusilo/drake,billhoffman/drake,manuelli/drake,thientu/drake,edowson/drake,psiorx/drake,tkoolen/drake,manuelli/drake,crogers3/drake,crogers3/drake,astrorog/drake,sheim/drake,hanssusilo/drake,tkoolen/drake,crogers3/drake,thientu/drake,thientu/drake,tkoolen/drake,sheim/drake,billhoffman/drake,crogers3/drake,edowson/drake,tkoolen/drake,sheim/drake,edowson/drake,edowson/drake