Callback to CPP & Leak Code

This checkin contains callbacks to cpp in bakcpp.cpp.
Building from that example I created leak.cpp. Both
of these files depend on leak.lua to test the
functionality of the code.

I am losing string variables in leak.cpp because the
string destructors are not being called because
the error is causing a long jump. Runnning valgrind
on both examples illustrates this point nicely.

In the next checking I will attempt to fix this
issue and then I will be ready to take a look
at Noah's code.