#unsetting: base utils/unsetting file for removing settings dependencies

an incremental approach to remove settings dependencies

This will follow up with two other pull requests which depend on this one.  This is the base.  the others depend on this one.  Those respectively begin an approach to remove dependencies to settings.py with a decorator.  utils/timezone is a straightforward example of using @uses_settings which is in here.  The other makes core/mail independent and is another canonical example of using @uses_settings() decorator which includes decorated class methods, etc.

This is the result of the djangocon sprint with help and work from Justin Holmes, Adrian and Jacob.  Thanks everyone!