Fixed equals() method and added hashCode() method for Fraction (both).
Fixed equals() method and added hashCode() method for Complex (both).
Changed HASH_PRIME's.
Fixed equals() method and added hashCode() method for PolyUnit (both).
Changed HASH_PRIME's to be different for each class.
Fixed equals() method and added hashCode() method for Polynomial (both).
Fixed equals() method and added hashCode() method for Matrix(both).