Implement CMappedList assign functions

[samirmenon]

1. Implement

// /** Example usage:
// * first.assign (7,100); // 7 ints with value 100
// * second.assign (first.begin(),first.end()); // a copy of first */
// void assign ( iterator first, iterator last );
// void assign ( size_type n, const T& u );

1. Implement unit tests