DNA_construct equality compares __repr__ instead of object instance

[dr3y]

DNA_construct is a Component but it has a different way of evaluating equality than a Component.

I did this because I don't want constructs with different data members (constructs that have or haven't been combinatorially enumerated) to be considered different (since they are, basically, the same construct and should yield the same combinatorial enumeration at the end).

However, it would be good if the equality method of all components was the same, so the suggested change is to change the equality function to something else and then use that everywhere where I am currently using equality.

I think this would involve a pretty significant number of changes to integrase_enumerator and DNA_construct and related things.