Fixed compiler compatibility problems

Hello,

I just recently got wind of the paper you presented on the Journal Track at ICAPS and man, it's AWESOME. My bad that I missed your talk in Portsmouth! I'll probably writing to you with questions sooner than later.

Just forked your repo and saw the problems you were having with the improved standards compliance of g++. Here I submit a very humble pull request for you to review. On the other hand, hunting those calls to _exit() would probably be a more long-term solution, but I think that a fix that intervenes the least in your code is the wisest approach.

Cheers,

Miquel.