When we eval with binding we will construct a new binding that
contains the original binding and that original binding will
construct a new evalDynamicScope.  If I do something like:

```ruby
p TOPLEVEL_BINDING.local_variable_defined? :c
p TOPLEVEL_BINDING.local_variable_defined? :_xxx_var_

b =TOPLEVEL_BINDING.dup
p b.local_variable_defined? :c
p b.local_variable_defined? :_xxx_var_
```

I should still see _xxx_var_ after the dup.  This will make that
do that but two different RubyBinding instances will end up
with the exact same backing Binding and I think this is wrong.
Landing anyways to see if anything breaks.

…ues but they will be their own thing from that point onward

…y will rename this from dup