Patched bug: enumeration_joint_ask gave wrong answers when the query variable overlaps the evidence.

Fixed: enumerate_joint_ask would raise KeyError on a combo of var values that didn't happen to be set. Though maybe this is too lenient, catching KeyError in ProbDist.__getitem__? (instead of in JointProbDist)

Agent.__init__ now takes a program parameter. A few more nonlocal-state-variable problems found and fixed. One agent program rewritten as a callable instance since it uses both state variables and abstract methods.

Moved agent-program definition back into the constructors to get rid of all the copying between parameters, instance vars, and nonlocals. Fixed nonlocal state-var bug in ReflexAgentWithState.

Some genetic_search() fixes: states were lists but had .mutate() called on them; pmut was probability of *not* mutating; initial population nonrandom; bad fitness function.