Fixing read_whole_problem_file bug

-  We fixed a couple of cyclic use calls in IO.pm
-  We moved not_null and pretty_print from PGcore into PGUtil and made
   a bunch of other changes to accomidate that
Fixed PGcore/not_null ref in AnswerHash
Changed fileFromPath back to standard importer stuff
Changed share to share_from with safe compartments.
revert unintended change
IMplementing MIkes fixes.
Further polish on pretty_print
Merge pull request #147 from goehle/readbug

Fixing read_whole_problem_file bug