A lot of minor codefixes

Andris!
1) Please, delete "public BasicBlock Clone(...)" method and use
Common.DeepClone(...) instead.
2) Do not use "internal" accessibility modifier, since it makes no sense
in our project environment (we do not have multiple assemblies). Use
public/private/(protected).
3) Why do you need GetVarFromCondition, GetRelopFromCondition,
GetConstFromCondition methods in Instruction class?
4) Why do you use parent.getSuccessors.First() as a "true successor"
(same for false). Is it a convention? If yes, I have to put it to
validator. :)

Vili:
1) Can you take "check_preceding_states" method out of Instruction class
(e.g. to DataAnalysis)?

Guys! Please use naming conventions for methods, e.g.
CheckPrecedingStates(...) instead of check_preceding_states(...), etc.