Revision 4918

Some bugfixes, preliminary commit of relax_restrict_ip function.  this
commit
 - adds relax_restrict_ip and hide_score_by_problem columns to the set
	and set_user tables
 - adds the corresponding fields to the Set and UserSet DB Records
 - patches 'no location' handling in the location management routine
	in CourseAdmin.pm
 - improves Authz->checkSet's handling of the case of location
	restriction when no addresses exist for a location, makes it
	use any cached set that may be available, and makes it honor
	relax_restrict_ip
 - corrects a typo and some comments in DB.pm
 - allows ip restriction fields in ProblemSetList when importing from
	or exporting to set definition files
 - updates ProblemSetDetail.pm to handle the relax_restrict_ip field

The relax_restrict_ip function has not been well tested.
hide_score_by_problem isn't yet used.