Method keyword arguments are destructive

ruby -v: jruby 9000.dev-SNAPSHOT (2.1.2p142) 2014-10-01 d3df63c Java HotSpot(TM) 64-Bit Server VM 24.65-b04 on 1.7.0_67-b01 [darwin-x86_64]

example:

``` ruby
def foo(bar: 'baz'); end
opts = {bar: 'something'}
foo(opts)
opts #=> {}
```

In MRI 2.1.3 the same code:

``` ruby
def foo(bar: 'baz'); end
opts = {bar: 'something'}
foo(opts)
opts #=> {:bar=>"something"}
```
