Hash#take_while wrong behavior in 1.7.19

``` ruby
passed = []
hash = {a: 1}
hash.take_while { |pair| passed << pair; true }
passed
# [:a] # jruby-1.7.19
# [[:a, 1]] # jruby-head
# [[:a, 1]] # mri-1.9.3
# [[:a, 1]] # mri-2.2.1
```

Thank you.
