Actually apply changes to limits and test_at.

The changes to limits and test_at were never applied, so the problems
sometimes fails to generate enough points (e.g. seed = 4857)

Author: lahvak

OpenProblemLibrary/AlfredUniv/anton8e/chapter1/1.5/prob9.pg

@@ -44,7 +44,7 @@ TEXT(beginproblem());
 
 $ans1 = Formula("1/sqrt(x**2 + 1)")->reduce;
 $ans2 = Formula("sqrt(1-1/x**2)")->reduce;
-$ans2->with(limits=>[1.1, 10], test_at=>[[-2],[-3]]);
+$ans2 = $ans2->with(limits=>[1.1, 10], test_at=>[[-2],[-3]]);
 
 Context()->texStrings;
 BEGIN_TEXT