#9 Add Prisoner's Dilemma problem

This is the problem that started it all, from Fujiki and
Dickinson’s 1987 paper on generating LISP programs. I
believe their implementation involved tests against a fixed set
of strategies, but it would also be good to offer another
Environment that tested all of the Individuals in the Population
against each other.

Problem Description: http://en.wikipedia.org/wiki/
Prisoner's_dilemma

The viewer mentioned here: http://sourceforge.net/tracker/
index.php?
func=detail&aid=1223651&group_id=140347&atid=745927 :
would be useful for this problem, allowing users to explore the
strategies generated in a better way than checking the
generated source file.