[Cs3] double dispatch example modified

[Mikhail Nesterenko]

CS3 students,

I was informed that as stated the Car Parts example was not
demonstrating double dispatch as the visitor (Inpsector and Operator)
was always explicitly stated.

I modified the example to have an array of visitors so the "accept"
method is indeed dispatched on the basis of both the calling element
and the visitor parameter.

Please take a look,
-- 
Mikhail