[WWcvs] pg: Only try to reduce intervals, sets and unions.

[dpvc v. a. <we...@ma...>]

Log Message:
-----------
Only try to reduce intervals, sets and unions.  (Don't call isReduced
on objects that don't support it).

Modified Files:
--------------
    pg/lib/Value:
        AnswerChecker.pm

Revision Data
-------------
Index: AnswerChecker.pm
===================================================================
RCS file: /webwork/cvs/system/pg/lib/Value/AnswerChecker.pm,v
retrieving revision 1.111
retrieving revision 1.112
diff -Llib/Value/AnswerChecker.pm -Llib/Value/AnswerChecker.pm -u -r1.111 -r1.112
--- lib/Value/AnswerChecker.pm
+++ lib/Value/AnswerChecker.pm
@@ -331,6 +331,7 @@
   return unless $ans->{studentsMustReduceUnions} &&
                 $ans->{showUnionReduceWarnings} &&
                 !$ans->{isPreview} && !Value::isFormula($student);
+  return unless $student->isSetOfReals;
   my ($result,$error) = $student->isReduced;
   return unless $error;
   return {