Trivial diff: fix tests/invalid/polymorphic_unification.err_exp

[Warwick Harvey]

My change to add a context to polymorphic unification error messages broke
the test for this error.  This patch fixes that error.


Estimated hours taken: 0.25

tests/invalid/polymorphic_unification.err_exp:
	Updated the expected error message to include context.


Index: tests/invalid/polymorphic_unification.err_exp
===================================================================
RCS file: /home/mercury1/repository/tests/invalid/polymorphic_unification.err_exp,v
retrieving revision 1.1
diff -u -r1.1 polymorphic_unification.err_exp
--- polymorphic_unification.err_exp     1998/11/09 05:28:39     1.1
+++ polymorphic_unification.err_exp     1998/12/15 01:14:36
@@ -1,2 +1,2 @@
-Software error: Sorry, not implemented: polymorphic unification in mode other than (in, in)
+Software error: polymorphic_unification.m:019: Sorry, not implemented: polymorphic unification in mode other than (in, in)
 Stack dump not available in this grade.