Each time a step_match is invoked it uses the same object as the step argument

As reported by [Daniel Esponda on the ML](https://groups.google.com/forum/#!topic/cukes/66-hQThZpMU)

I've created an [example of this for cucumber 2.0](https://github.com/tooky/cucumber-reuse-params).

Cucumber 2.0 is different because the step arguments are frozen, but I do think its unexpected that we get the same `===` object each time a particular step match is run. Is it also slightly problematic if users can't modify step arguments because they are frozen?