callback, then only modifies AH to exit to DOS. meanwhile the Program
object now contains an exit status and a function to write the exit
status to the AL register. This means the builtin DOSBox programs are
now capable of exiting to DOS with a nonzero exit code. All that needs
to be done now is to have the shell and DOS programs built into DOSBox
return proper error codes when things go wrong. Added code to test this
new mechanism by typing "config -errtest" which should return error code
1.
