This evals the attributd sub, and checks for an 
eval on the stack if it dies. If there is one 
then the exception is propagated via "die $@";
if not then cluck is used to dump a stack trace
and the error message.

Exceptions can be forced through a specific 
perl function (via A::B) or class call 
(via Class->method). The tests give examples 
of various ways to set the calls up.

This is useful for sub's that know they throw what
should be non-fatal exceptions or for calls inside
of long-running processes that need to decide quickly
if they have been called properly. It can also be 
useful for modules that use modules that use Fatal,
which can lead to the code issuing exceptions that
aren't explicit in the code.