Fixed compile error with internal class

Hi Guillaume,
This is Derek with Gabor Marth's group @ Boston College. We've integrated Jellyfish into our unified analysis pipeline/launcher project, GKNO (www.gkno.me , https://github.com/gkno/gkno_launcher ). Feel free to ping back with any questions, comments, concerns, suggestions, etc.

I came across a compile error while on 2 of our machines (both using gcc 4.6.3). My fix is in this pull request. 

Thanks,
  - Derek