Consider this snippet:

class Container
    def field=(val)
        puts self.field
        @field = val
    end

    def field
        @field
    end
end

def m()
    var = Container.new
    var.field = "hello"
    puts var.field
end

With the existing formulation of basicStoreStep, we would track flow from "hello" into self.field in the setter, because the target of the store was the pre-update node and not the post-update node. However, we actually didn't have any flow, since basicStoreStep was erroneously restricted to target only local source nodes. The second commit introduces the false flow (and the correct missing flow) by removing the local-source-node restriction, and the last commit removes the false flow by targeting post-update nodes.

@tausbn : AFAICT, the Python implementation also doesn't use post-update nodes, but perhaps there it is not a problem, if the pre-update node may not flow into a call like above.