Unifying Exception types in setup

[Max Bowsher]

Robert,

Currently setup uses both <stdexcept> exceptions, and its own
std::exception-derived Exceptions.

I'm about to write a patch to convert the kludgy

if (error)
    exit(some_random_exit_code);

bits to exceptions. Which kind shall I use, and would you be interested in a
patch to convert all of them over to one kind?

Max.