This allows for on_* to be defined by defining the corresponding instance method

directly.  Prior to this fix, doing this will result in "SystemStackError: stack
level too deep".

Example
module RedStorm
  module Examples
    class SplitSentenceBolt < DSL::Bolt
      def on_receive(tuple)
        tuple[0].split(' ').map{|w| [w]}
      end
    end
  end
end
(For similar reasons, I'm removing the BoltError you suggested - see use case:

```ruby
class SomeBolt
  on_receive :ack => false
  def on_receive(tuple) ; end
end
```
)