Changing behaviour so that instead of rebinding after a successful
migration and continuing as an ordinary server, we simply quit with a
0 exit code and let our caller restart us as a server if they want to.
This means that everything in listen.c, listen.h, and anything making
reference to a rebind address is unneeded.
Previously, the --verbose flag was only present in debug builds. Now
it's present whether you define DEBUG or not. What changes is the
amount of information printed to stderr: DEBUG sets the --verbose log
level to 0 (debug), while DEBUG unset sets it to 1 (info). This makes
driving the binary slightly simpler as you don't have to detect whether
it's a debug build by scanning for "--verbose" in the help output.
