Restore missing imports
Updated this error string; though this function will likely be removed at some point.
Add a helpers function for getting info out of the package's .version module; previously this was returning the version module in astropy_helpers itself.  This changes the get_debug_option function such that it requires the package name.  Will probably refactor functions like that into a class that is already instatiated with basic info about the package being built, such as its name.
Removing the last vestiges of the astropy config system for now, as it won't work with astropy_helpers in its current state.  This can, and should be revisited once we have a better idea of what we're going to do about configuration.