Revision 4909

Second preliminary commit of changes to move set-level valid checks to
Authz.  This makes ProblemSet.pm and Problem.pm use the
$self->{invalidSet} value set by ContentGenerator.pm, and means that
regular homework assignments may now be restricted to specific IP
addresses.  This commit also corrects $userName/$effectiveUserName
errors I had in Authz->checkSet() and moves the actual IP address
checking to a separate subroutine in Authz.  Hardcopy.pm uses that
routine to filter sets to be sure it doesn't generate hardcopies for
a IP address restricted set.