Avoid overflows to avoid panic

[dfquaresma]

Looking at the worst scenario, some integer variables could overflow while GCI run. Counters around the code and the variables incoming and finished, in interceptor.go file, are examples of it.
One solution for it would be turn them for zero at some moment. To incoming and finished it could be done after each GC execution.

[danielfireman]

Also, a great time to start adding tests. Those test scenarios are could be used when porting GCI to other runtimes.