Don't blow the stack on JRuby

The Defaults class was making an assumption about the return value of
Array#reverse that doesn't hold up on JRuby nor will it on Ruby 2.1
once that comes out. Calling to_a after reverse ensures we have an
actual Array object so we don't recursively call the overridden each
method until things blow up.
Merge pull request #26 from bbrowning/jruby_stack_blown

Don't blow the stack on JRuby