facebook usrbincrash php implementation

Implementation for Facebook usr bin crash puzzle. (how/why)

I haven't touched the code for a few months, but better to put it online then to let it rot.
http://github.com/Dieterbe/facebookpuzzles/

2 branches:

• master: basically what I submitted to FB, and what just works
• withpruning: an attempt for futher optimalisation (it only improves the runtime in some cases) but I didn't finish that version and there's a bug in it somewhere

In the repo you'll also find various test input files supplied by the community on the forums and a script to benchmark the implementation on all inputfiles.