[WWcvs] pg: Prevent error message when num_cmp specifies the same string more

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

Log Message:
-----------
Prevent error message when num_cmp specifies the same string more than
once (e.g., upper and lower case versions of the same thing).

Modified Files:
--------------
    pg/macros:
        PGanswermacros.pl

Revision Data
-------------
Index: PGanswermacros.pl
===================================================================
RCS file: /webwork/cvs/system/pg/macros/PGanswermacros.pl,v
retrieving revision 1.48
retrieving revision 1.49
diff -Lmacros/PGanswermacros.pl -Lmacros/PGanswermacros.pl -u -r1.48 -r1.49
--- macros/PGanswermacros.pl
+++ macros/PGanswermacros.pl
@@ -1080,7 +1080,8 @@
 	  foreach my $string (@{$num_params{strings}}) {
 	    my %tex = ($string =~ m/^(-?)inf(inity)?$/i)? (TeX => "$1\\infty"): ();
 	    %tex = (TeX => "-\\infty") if uc($string) eq "MINF";
-	    $context->strings->add(uc($string) => {%tex});
+	    $context->strings->add(uc($string) => {%tex})
+	      unless $context->strings->get(uc($string));
 	  }
 	}