Move answer stringification after content post processing.

This is so that the content post processor methods have access to the
full answer objects.  This gives this approach a whole lot more power
than the (soon to be eliminated) results table has.

lib/WeBWorK/PG.pm

@@ -184,6 +184,7 @@ sub new_helper ($invocant, %options) {
 	}
 
 	$translator->post_process_content;
+	$translator->stringify_answers;
 
 	return bless {
 		translator       => $translator,

lib/WeBWorK/PG/Translator.pm

@@ -49,6 +49,7 @@ WeBWorK::PG::Translator - Evaluate PG code and evaluate answers safely
     my $rh_problem_result = $pt->grade_problem(%options); # grades the problem.
 
     $pt->post_process_content;   # Execute macro or problem hooks that further modify the problem content.
+    $pt->stringify_answers;      # Convert objects to strings in the answer hash
 
 =head1 DESCRIPTION
 
@@ -1059,7 +1060,6 @@ sub grade_problem {
 	use strict;
 
 	die $@ if $@;
-	$self->stringify_answers;
 	return ($self->{rh_problem_result}, $self->{rh_problem_state});
 }