[Cs3] using plus functor for strings

[Mikhail Nesterenko]

CS3 students,

There was a question in class about using predefined functor plus for
string concatenation. It works as expected. Here is an example:

   http://vega.cs.kent.edu/~mikhail/classes/cs3/Examples/STLAlgorithms/Functors/strings.cpp

Thanks,
--
Mikhail