Different results for `to_h` and `to_hash` on `ENV`

Hi,

converting `ENV` to a `Hash` gives different results. It depends on which `to_`-method is used.

_MRI_

``` ruby
ENV.object_id
# => 17981260
ENV.to_h.object_id
# => 22183040
ENV.to_hash.object_id
# => 22148380
```

_JRuby_

``` ruby
ENV.object_id
# => 2042
ENV.to_h.object_id
# => 2042
ENV.to_hash.object_id
# => 2044
```
