Jruby fixes

Here are some fixes I had to do to get dullard working with jruby.

There isn't great documentation and no tests yet, I may do that later on. Let me know what you think.
Is there any way to do this in a backwards compatible way? Maybe 
```
enum = Enumerator.new do |y| 
  ...
end
def enum.size
  row_count
end
enum
```