configuration snapshot & comparison

[petersilva]

Issues that would be addressed by this: #35 #618 #895 #912

I've long thought that we should detect config changes on startup... as in
pickle a config in the state directory after starting.
when parsing the config, compare the result to the pickle.
process differences:
put retry in re-filter mode...if accepts or directories have changed...
delete bindings on queue if they are no longer in the config.
probably a whole different issue.