CSequence uses std::find, and CCollection uses the more efficient find method of the implementation type,
which requires that the implementation type be an associative container like QSet or std::set.
Modified CContainerBase::contains to use these new find methods.
The new compare is implemented using "multimethods" described in the book Advanced C++ Programming Styles and Idioms by James Coplien.
First, the isA method is used to determine which of the values being compared is the most general. (For example, CLength is more general than CAltitude.)
Then the compareImpl method is called on the most general value, with the other value as an argument.
If there is not a direct inheritance relation between the two values (or they are the same class) then the comparison is invalid and a assert is triggered.
